diff --git a/questsions_dict.py b/questsions_dict.py
index f8049b4..f66efc9 100644
--- a/questsions_dict.py
+++ b/questsions_dict.py
@@ -1,1163 +1,671 @@
 
 qha = {
-    "q1": "1. Import the numpy package under the name `np` (★☆☆)",
+    "q1": "Import the numpy package under the name `np` (★☆☆)",
     "h1": "hint: import … as ",
     "a1":
 """
 import numpy as np
 """,
-    "q2": "2. Print the numpy version and the configuration (★☆☆)",
+    "q2": "Print the numpy version and the configuration (★☆☆)",
     "h2": "hint: np.__version__, np.show_config)",
     "a2":
 """
 
 """,
-    "q3": "3. Create a null vector of size 10 (★☆☆)",
+    "q3": "Create a null vector of size 10 (★☆☆)",
     "h3": "hint: np.zeros",
     "a3":
 """
 
 """,
-    "q4": "4.  How to find the memory size of any array (★☆☆)",
+    "q4": "How to find the memory size of any array (★☆☆)",
     "h4": "hint: size, itemsize",
     "a4":
 """
 
 """,
-    "q5": "5.  How to get the documentation of the numpy add function from the command line? (★☆☆)",
+    "q5": "How to get the documentation of the numpy add function from the command line? (★☆☆)",
     "h5": "hint: np.info",
     "a5":
 """
 
 """,
-    "q6": "6.  Create a null vector of size 10 but the fifth value which is 1 (★☆☆)",
+    "q6": "Create a null vector of size 10 but the fifth value which is 1 (★☆☆)",
     "h6": "hint: array[4]",
     "a6":
 """
 
 """,
-    "q7": "7.  Create a vector with values ranging from 10 to 49 (★☆☆)",
+    "q7": "Create a vector with values ranging from 10 to 49 (★☆☆)",
     "h7": "hint: arange",
     "a7":
 """
 
 """,
-    "q8": "8.  Reverse a vector (first element becomes last) (★☆☆)",
+    "q8": "Reverse a vector (first element becomes last) (★☆☆)",
     "h8": "hint: array[::-1]",
     "a8":
 """
 
 """,
-    "q9": "9.  Create a 3x3 matrix with values ranging from 0 to 8 (★☆☆)",
+    "q9": "Create a 3x3 matrix with values ranging from 0 to 8 (★☆☆)",
     "h9": "hint: reshape",
     "a9":
 """
 
 """,
-    "q10": "10. Find indices of non-zero elements from [1,2,0,0,4,0] (★☆☆)",
+    "q10": "Find indices of non-zero elements from [1,2,0,0,4,0] (★☆☆)",
     "h10": "hint: np.nonzero",
     "a10":
 """
 
 """,
-    "q11": "11. Create a 3x3 identity matrix (★☆☆)",
+    "q11": "Create a 3x3 identity matrix (★☆☆)",
     "h11": "hint: np.eye",
     "a11":
 """
 
 """,
-    "q12": "12. Create a 3x3x3 array with random values (★☆☆)",
+    "q12": "Create a 3x3x3 array with random values (★☆☆)",
     "h12": "hint: np.random.random",
     "a12":
 """
 
 """,
-    "q13": "",
-    "h13": "hint: ",
+    "q13": "Create a 10x10 array with random values and find the minimum and maximum values (★☆☆)",
+    "h13": "hint: min, max",
     "a13":
 """
 
 """,
-    "q14": "",
-    "h14": "hint: ",
+    "q14": "Create a random vector of size 30 and find the mean value (★☆☆)",
+    "h14": "hint: mean",
     "a14":
 """
 
 """,
-    "q15": "",
-    "h15": "hint: ",
+    "q15": "Create a 2d array with 1 on the border and 0 inside (★☆☆)",
+    "h15": "hint: array[1:-1, 1:-1]",
     "a15":
 """
 
 """,
-    "q16": "",
-    "h16": "hint: ",
+    "q16": "How to add a border (filled with 0's) around an existing array? (★☆☆)",
+    "h16": "hint: np.pad",
     "a16":
 """
 
 """,
-    "q17": "",
-    "h17": "hint: ",
+    "q17": """
+What is the result of the following expression? (★☆☆)"
+```python
+0 * np.nan
+np.nan == np.nan
+np.inf > np.nan
+np.nan - np.nan
+np.nan in set([np.nan])
+# 0.3 == 3 * 0.1
+# ```""",
+    "h17": "hint: NaN = not a number, inf = infinity",
     "a17":
 """
 
 """,
-    "q18": "",
-    "h18": "hint: ",
+    "q18": "Create a 5x5 matrix with values 1,2,3,4 just below the diagonal (★☆☆)",
+    "h18": "hint: np.diag",
     "a18":
 """
 
 """,
-    "q19": "",
-    "h19": "hint: ",
+    "q19": "Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)",
+    "h19": "hint: array[::2]",
     "a19":
 """
 
 """,
-    "q20": "",
-    "h20": "hint: ",
+    "q20": "Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?",
+    "h20": "hint: np.unravel_index",
     "a20":
 """
 
 """,
-    "q21": "",
-    "h21": "hint: ",
+    "q21": "Create a checkerboard 8x8 matrix using the tile function (★☆☆)",
+    "h21": "hint: np.tile",
     "a21":
 """
 
 """,
-    "q22": "",
-    "h22": "hint: ",
+    "q22": "Normalize a 5x5 random matrix (★☆☆)",
+    "h22": "hint: (x -mean)/std",
     "a22":
 """
 
 """,
-    "q23": "",
-    "h23": "hint: ",
+    "q23": "Create a custom dtype that describes a color as four unsigned bytes (RGBA) (★☆☆)",
+    "h23": "hint: np.dtype",
     "a23":
 """
 
 """,
-    "q24": "",
+    "q24": "Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)",
     "h24": "hint: ",
     "a24":
 """
 
 """,
-    "q25": "",
-    "h25": "hint: ",
+    "q25": "Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)",
+    "h25": "hint: >, <=",
     "a25":
 """
 
 """,
-    "q26": "",
-    "h26": "hint: ",
+    "q26": """
+What is the output of the following script? (★☆☆)
+```python
+# Author: Jake VanderPlas
+
+print(sum(range(5),-1))
+from numpy import *
+print(sum(range(5),-1))
+```
+""",
+    "h26": "hint: np.sum",
     "a26":
 """
 
 """,
-    "q27": "",
-    "h27": "hint: ",
+    "q27": """
+Consider an integer vector Z, which of these expressions are legal? (★☆☆)
+```python
+Z**Z
+2 << Z >> 2
+Z <- Z
+1j*Z
+Z/1/1
+Z<Z>Z
+```""",
+    "h27": "No hints provided...",
     "a27":
 """
 
 """,
-    "q28": "",
-    "h28": "hint: ",
+    "q28": """
+What are the result of the following expressions?
+```python
+np.array(0) / np.array(0)
+np.array(0) // np.array(0)
+np.array([np.nan]).astype(int).astype(float)
+```
+""",
+
+    "h28": "No hints provided... ",
     "a28":
 """
 
 """,
-    "q29": "",
-    "h29": "hint: ",
+    "q29": "How to round away from zero a float array ? (★☆☆)",
+    "h29": "hint: np.uniform, np.copysign, np.ceil, np.abs",
     "a29":
 """
 
 """,
-    "q30": "",
-    "h30": "hint: ",
+    "q30": "How to find common values between two arrays? (★☆☆)",
+    "h30": "hint: np.intersect1d",
     "a30":
 """
 
 """,
-    "q31": "",
-    "h31": "hint: ",
+    "q31": "How to ignore all numpy warnings (not recommended)? (★☆☆)",
+    "h31": "hint: np.seterr, np.errstate",
     "a31":
 """
 
 """,
-    "q32": "",
-    "h32": "hint: ",
+    "q32": """
+Is the following expressions true? (★☆☆)
+```python
+np.sqrt(-1) == np.emath.sqrt(-1)
+```
+""",
+    "h32": "hint: imaginary number",
     "a32":
 """
 
 """,
-    "q33": "",
-    "h33": "hint: ",
+    "q33": "How to get the dates of yesterday, today and tomorrow? (★☆☆)",
+    "h33": "hint: np.datetime64, np.timedelta64",
     "a33":
 """
 
 """,
-    "q34": "",
-    "h34": "hint: ",
+    "q34": "How to get all the dates corresponding to the month of July 2016? (★★☆)",
+    "h34": "hint: np.arange(dtype=datetime64['D'])",
     "a34":
 """
 
 """,
-    "q35": "",
-    "h35": "hint: ",
+    "q35": "How to compute ((A+B)*(-A/2)) in place (without copy)? (★★☆)",
+    "h35": "hint: np.add(out=), np.negative(out=), np.multiply(out=), np.divide(out=)",
     "a35":
 """
 
 """,
-    "q36": "",
-    "h36": "hint: ",
+    "q36": "Extract the integer part of a random array using 5 different methods (★★☆)",
+    "h36": "hint: %, np.floor, np.ceil, astype, np.trunc",
     "a36":
 """
 
 """,
-    "q37": "",
-    "h37": "hint: ",
+    "q37": "Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)",
+    "h37": "hint: np.arange",
     "a37":
 """
 
 """,
-    "q38": "",
-    "h38": "hint: ",
+    "q38": "Consider a generator function that generates 10 integers and use it to build an array (★☆☆)",
+    "h38": "hint: np.fromiter",
     "a38":
 """
 
 """,
-    "q39": "",
-    "h39": "hint: ",
+    "q39": "Create a vector of size 10 with values ranging from 0 to 1, both excluded (★★☆)",
+    "h39": "hint: np.linspace",
     "a39":
 """
 
 """,
-    "q40": "",
-    "h40": "hint: ",
+    "q40": "Create a random vector of size 10 and sort it (★★☆)",
+    "h40": "hint: sort",
     "a40":
 """
 
 """,
-    "q41": "",
-    "h41": "hint: ",
+    "q41": "How to sum a small array faster than np.sum? (★★☆)",
+    "h41": "hint: np.add.reduce",
     "a41":
 """
 
 """,
-    "q42": "",
-    "h42": "hint: ",
+    "q42": "Consider two random array A and B, check if they are equal (★★☆)",
+    "h42": "hint: np.allclose, np.array_equal",
     "a42":
 """
 
 """,
-    "q43": "",
-    "h43": "hint: ",
+    "q43": "Make an array immutable (read-only) (★★☆)",
+    "h43": "hint: flags.writeable",
     "a43":
 """
 
 """,
-    "q44": "",
-    "h44": "hint: ",
+    "q44": "Consider a random 10x2 matrix representing cartesian coordinates, convert them to polar coordinates (★★☆)",
+    "h44": "hint: np.sqrt, np.arctan2",
     "a44":
 """
 
 """,
-    "q45": "",
-    "h45": "hint: ",
+    "q45": "Create random vector of size 10 and replace the maximum value by 0 (★★☆)",
+    "h45": "hint: argmax",
     "a45":
 """
 
 """,
-    "q46": "",
-    "h46": "hint: ",
+    "q46": "Create a structured array with `x` and `y` coordinates covering the [0,1]x[0,1] area (★★☆)",
+    "h46": "hint: np.meshgrid",
     "a46":
 """
 
 """,
-    "q47": "",
-    "h47": "hint: ",
+    "q47": "Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))",
+    "h47": "hint: np.subtract.outer",
     "a47":
 """
 
 """,
-    "q48": "",
-    "h48": "hint: ",
+    "q48": "Print the minimum and maximum representable value for each numpy scalar type (★★☆)",
+    "h48": "hint: np.iinfo, np.finfo, eps",
     "a48":
 """
 
 """,
-    "q49": "",
-    "h49": "hint: ",
+    "q49": "How to print all the values of an array? (★★☆)",
+    "h49": "hint: np.set_printoptions",
     "a49":
 """
 
 """,
-    "q50": "",
-    "h50": "hint: ",
+    "q50": "How to find the closest value (to a given scalar) in a vector? (★★☆)",
+    "h50": "hint: argmin",
     "a50":
 """
 
 """,
-    "q51": "",
-    "h51": "hint: ",
+    "q51": "Create a structured array representing a position (x,y) and a color (r,g,b) (★★☆)",
+    "h51": "hint: dtype",
     "a51":
 """
 
 """,
-    "q52": "",
-    "h52": "hint: ",
+    "q52": "Consider a random vector with shape (100,2) representing coordinates, find point by point distances (★★☆)",
+    "h52": "hint: np.atleast_2d, T, np.sqrt",
     "a52":
 """
 
 """,
-    "q53": "",
-    "h53": "hint: ",
+    "q53": "How to convert a float (32 bits) array into an integer (32 bits) in place?",
+    "h53": "hint: astype(copy=False)",
     "a53":
 """
 
 """,
-    "q54": "",
-    "h54": "hint: ",
+    "q54": """
+How to read the following file? (★★☆)
+```
+1, 2, 3, 4, 5
+6,  ,  , 7, 8
+ ,  , 9,10,11
+```
+""",
+    "h54": "hint: np.genfromtxt",
     "a54":
 """
 
 """,
-    "q55": "",
-    "h55": "hint: ",
+    "q55": "What is the equivalent of enumerate for numpy arrays? (★★☆)",
+    "h55": "hint: np.ndenumerate, np.ndindex",
     "a55":
 """
 
 """,
-    "q56": "",
-    "h56": "hint: ",
+    "q56": "Generate a generic 2D Gaussian-like array (★★☆)",
+    "h56": "hint: np.meshgrid, np.exp",
     "a56":
 """
 
 """,
-    "q57": "",
-    "h57": "hint: ",
+    "q57": "How to randomly place p elements in a 2D array? (★★☆)",
+    "h57": "hint: np.put, np.random.choice",
     "a57":
 """
 
 """,
-    "q58": "",
-    "h58": "hint: ",
+    "q58": "Subtract the mean of each row of a matrix (★★☆)",
+    "h58": "hint: mean(axis=,keepdims=)",
     "a58":
 """
 
 """,
-    "q59": "",
-    "h59": "hint: ",
+    "q59": "How to sort an array by the nth column? (★★☆)",
+    "h59": "hint: argsort",
     "a59":
 """
 
 """,
 
-    "q60": "",
-    "h60": "hint: ",
+    "q60": "How to tell if a given 2D array has null columns? (★★☆)",
+    "h60": "hint: any, ~",
     "a60":
 """
 
 """,
-    "q61": "",
-    "h61": "hint: ",
+    "q61": "Find the nearest value from a given value in an array (★★☆)",
+    "h61": "hint: np.abs, argmin, flat",
     "a61":
 """
 
 """,
-    "q62": "",
-    "h62": "hint: ",
+    "q62": "Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? (★★☆)",
+    "h62": "hint: np.nditer",
     "a62":
 """
 
 """,
-    "q63": "",
-    "h63": "hint: ",
+    "q63": "Create an array class that has a name attribute (★★☆)",
+    "h63": "hint: class method",
     "a63":
 """
 
 """,
-    "q64": "",
-    "h64": "hint: ",
+    "q64": "Consider a given vector, how to add 1 to each element indexed by a second vector "
+           "(be careful with repeated indices)? (★★★)",
+    "h64": "hint: np.bincount | np.add.at",
     "a64":
 """
 
 """,
-    "q65": "",
-    "h65": "hint: ",
+    "q65": "How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)",
+    "h65": "hint: np.bincount",
     "a65":
 """
 
 """,
-    "q66": "",
-    "h66": "hint: ",
+    "q66": "Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique colors (★★★)",
+    "h66": "hint: np.unique",
     "a66":
 """
 
 """,
-    "q67": "",
-    "h67": "hint: ",
+    "q67": "Considering a four dimensions array, how to get sum over the last two axis at once? (★★★)",
+    "h67": "hint: sum(axis=(-2,-1))",
     "a67":
 """
 
 """,
-    "q68": "",
-    "h68": "hint: ",
+    "q68": "Considering a one-dimensional vector D, how to compute means of subsets of D using a vector S "
+           "of same size describing subset  indices? (★★★)",
+    "h68": "hint: np.bincount",
     "a68":
 """
 
 """,
-    "q69": "",
-    "h69": "hint: ",
+    "q69": "How to get the diagonal of a dot product? (★★★)",
+    "h69": "hint: np.diag",
     "a69":
 """
 
 """,
-    "q70": "",
-    "h70": "hint: ",
+    "q70": "Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3 consecutive "
+           "zeros interleaved between each value? (★★★)",
+    "h70": "hint: array[::4]",
     "a70":
 """
 
 """,
-    "q71": "",
-    "h71": "hint: ",
+    "q71": "Consider an array of dimension (5,5,3), how to mulitply it by an array with dimensions (5,5)? (★★★)",
+    "h71": "hint: array[:, :, None]",
     "a71":
 """
 
 """,
-    "q72": "",
-    "h72": "hint: ",
+    "q72": "How to swap two rows of an array? (★★★)",
+    "h72": "hint: array[[]] = array[[]]",
     "a72":
 """
 
 """,
-    "q73": "",
-    "h73": "hint: ",
+    "q73": "Consider a set of 10 triplets describing 10 triangles (with shared vertices), find the "
+           "set of unique line segments composing all the  triangles (★★★)",
+    "h73": "hint: repeat, np.roll, np.sort, view, np.unique",
     "a73":
 """
 
 """,
-    "q74": "",
-    "h74": "hint: ",
+    "q74": "Given an array C that is a bincount, how to produce an array A such that np.bincount(A) == C? (★★★)",
+    "h74": "hint: np.repeat",
     "a74":
 """
 
 """,
-    "q75": "",
-    "h75": "hint: ",
+    "q75": "How to compute averages using a sliding window over an array? (★★★)",
+    "h75": "hint: np.cumsum",
     "a75":
 """
 
 """,
-    "q76": "",
-    "h76": "hint: ",
+    "q76": "Consider a one-dimensional array Z, build a two-dimensional array whose first row is "
+           "(Z[0],Z[1],Z[2]) and each subsequent row is  shifted by 1 (last row should be "
+           "(Z[-3],Z[-2],Z[-1]) (★★★)",
+    "h76": "hint: from numpy.lib import stride_tricks",
     "a76":
 """
 
 """,
-    "q77": "",
-    "h77": "hint: ",
+    "q77": "How to negate a boolean, or to change the sign of a float inplace? (★★★)",
+    "h77": "hint: np.logical_not, np.negative",
     "a77":
 """
 
 """,
 
-    "q78": "",
-    "h78": "hint: ",
+    "q78": "Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to compute "
+           "distance from p to each line i (P0[i],P1[i])? (★★★)",
+    "h78": "No hints provided...",
     "a78":
 """
 
 """,
-    "q79": "",
-    "h79": "hint: ",
+    "q79": "Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P, how to "
+           "compute distance from each point j (P[j]) to each line i (P0[i],P1[i])? (★★★)",
+    "h79": "No hints provided...",
     "a79":
 """
 
 """,
-    "q80": "",
-    "h80": "hint: ",
+    "q80": "Consider an arbitrary array, write a function that extract a subpart with a fixed "
+           "shape and centered on a given element (pad with a `fill` value when necessary) (★★★)",
+    "h80": "hint: minimum maximum",
     "a80":
 """
 
 """,
-    "q81": "",
-    "h81": "hint: ",
+    "q81": "Consider an array Z = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to "
+           "generate an array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]]? (★★★)",
+    "h81": "hint: stride_tricks.as_strided",
     "a81":
 """
 
 """,
-    "q82": "",
-    "h82": "hint: ",
+    "q82": "Compute a matrix rank (★★★) ",
+    "h82": "hint: np.linalg.svd",
     "a82":
 """
 
 """,
-    "q83": "",
-    "h83": "hint: ",
+    "q83": "How to find the most frequent value in an array?",
+    "h83": "hint: np.bincount, argmax",
     "a83":
 """
 
 """,
-    "q84": "",
-    "h84": "hint: ",
+    "q84": "Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)",
+    "h84": "hint: stride_tricks.as_strided",
     "a84":
 """
 
 """,
-    "q85": "",
-    "h85": "hint: ",
+    "q85": "Create a 2D array subclass such that Z[i,j] == Z[j,i] (★★★)",
+    "h85": "hint: class method",
     "a85":
 """
 
 """,
-    "q86": "",
-    "h86": "hint: ",
+    "q86": "Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1). "
+           "How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)",
+    "h86": "hint: np.tensordot",
     "a86":
 """
 
 """,
-    "q87": "",
-    "h87": "hint: ",
+    "q87": "Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)",
+    "h87": "hint: np.add.reduceat",
     "a87":
 """
 
 """,
 
-    "q88": "",
-    "h88": "hint: ",
+    "q88": "How to implement the Game of Life using numpy arrays? (★★★)",
+    "h88": "No hints provided... ",
     "a88":
 """
 
 """,
-    "q89": "",
-    "h89": "hint: ",
+    "q89": "How to get the n largest values of an array (★★★)",
+    "h89": "hint: np.argsort | np.argpartition",
     "a89":
 """
 
 """,
-    "q90": "",
-    "h90": "hint: ",
+    "q90": "Given an arbitrary number of vectors, build the cartesian product "
+           "(every combinations of every item) (★★★)",
+    "h90": "hint: np.indices",
     "a90":
 """
 
 """,
-    "q91": "",
-    "h91": "hint: ",
+    "q91": "How to create a record array from a regular array? (★★★)",
+    "h91": "hint: np.core.records.fromarrays",
     "a91":
 """
 
 """,
-    "q92": "",
-    "h92": "hint: ",
+    "q92": "Consider a large vector Z, compute Z to the power of 3 using 3 different methods (★★★)",
+    "h92": "hint: np.power, *, np.einsum",
     "a92":
 """
 
 """,
-    "q93": "",
-    "h93": "hint: ",
+    "q93": "Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A "
+           "that contain elements of each row of B regardless of the order of the elements in B? (★★★)",
+    "h93": "hint: np.where",
     "a93":
 """
 
 """,
-    "q94": "",
-    "h94": "hint: ",
+    "q94": "Considering a 10x3 matrix, extract rows with unequal values (e.g. [2,2,3]) (★★★)",
+    "h94": "No hints provided...",
     "a94":
 """
 
 """,
-    "q95": "",
-    "h95": "hint: ",
+    "q95": "Convert a vector of ints into a matrix binary representation (★★★)",
+    "h95": "hint: np.unpackbits",
     "a95":
 """
 
 """,
-    "q96": "",
-    "h96": "hint: ",
+    "q96": "Given a two dimensional array, how to extract unique rows? (★★★)",
+    "h96": "hint: np.ascontiguousarray | np.unique",
     "a96":
 """
 
 """,
-    "q97": "",
-    "h97": "hint: ",
+    "q97": "Considering 2 vectors A & B, write the einsum equivalent of inner, outer, sum, and mul function (★★★)",
+    "h97": "hint: np.einsum",
     "a97":
 """
 
 """,
 
-    "q98": "",
-    "h98": "hint: ",
+    "q98": "Considering a path described by two vectors (X,Y), how to sample it using equidistant samples (★★★)?",
+    "h98": "hint: np.cumsum, np.interp ",
     "a98":
 """
 
 """,
-    "q99": "",
-    "h99": "hint: ",
+    "q99": "Given an integer n and a 2D array X, select from X the rows which can be interpreted as draws "
+           "from a multinomial distribution with n degrees, i.e., the rows which only contain integers "
+           "and which sum to n. (★★★)",
+    "h99": "hint: np.logical_and.reduce, np.mod",
     "a99":
 """
 
 """,
-    "q100": "",
-    "h100": "hint: ",
+    "q100": "Compute bootstrapped 95% confidence intervals for the mean of a 1D array X (i.e., "
+            "resample the elements of an array with replacement N times, compute the mean of "
+            "each sample, and then compute percentiles over the means). (★★★)",
+    "h100": "hint: np.percentile",
     "a100":
 """
 
 """,
 }
-# ####
-#
-# (**hint**: np.random.random)
-#
-#
-#
-# #### 13. Create a 10x10 array with random values and find the minimum and maximum values (★☆☆)
-#
-# (**hint**: min, max)
-#
-#
-#
-# #### 14. Create a random vector of size 30 and find the mean value (★☆☆)
-#
-# (**hint**: mean)
-#
-#
-#
-# #### 15. Create a 2d array with 1 on the border and 0 inside (★☆☆)
-#
-# (**hint**: array\[1:-1, 1:-1\])
-#
-#
-#
-# #### 16. How to add a border (filled with 0's) around an existing array? (★☆☆)
-#
-# (**hint**: np.pad)
-#
-#
-#
-# #### 17. What is the result of the following expression? (★☆☆)
-#
-# (**hint**: NaN = not a number, inf = infinity)
-#
-#
-# ```python
-# 0 * np.nan
-# np.nan == np.nan
-# np.inf > np.nan
-# np.nan - np.nan
-# np.nan in set([np.nan])
-# 0.3 == 3 * 0.1
-# ```
-#
-# #### 18. Create a 5x5 matrix with values 1,2,3,4 just below the diagonal (★☆☆)
-#
-# (**hint**: np.diag)
-#
-#
-#
-# #### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)
-#
-# (**hint**: array\[::2\])
-#
-#
-#
-# #### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
-#
-# (**hint**: np.unravel\_index)
-#
-#
-#
-# #### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)
-#
-# (**hint**: np.tile)
-#
-#
-#
-# #### 22. Normalize a 5x5 random matrix (★☆☆)
-#
-# (**hint**: (x - mean) / std)
-#
-#
-#
-# #### 23. Create a custom dtype that describes a color as four unsigned bytes (RGBA) (★☆☆)
-#
-# (**hint**: np.dtype)
-#
-#
-#
-# #### 24. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)
-#
-# (**hint**: np.dot | @)
-#
-#
-#
-# #### 25. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)
-#
-# (**hint**: >, <=)
-#
-#
-#
-# #### 26. What is the output of the following script? (★☆☆)
-#
-# (**hint**: np.sum)
-#
-#
-# ```python
-# # Author: Jake VanderPlas
-#
-# print(sum(range(5),-1))
-# from numpy import *
-# print(sum(range(5),-1))
-# ```
-#
-# #### 27. Consider an integer vector Z, which of these expressions are legal? (★☆☆)
-#
-#
-# ```python
-# Z**Z
-# 2 << Z >> 2
-# Z <- Z
-# 1j*Z
-# Z/1/1
-# Z<Z>Z
-# ```
-#
-# #### 28. What are the result of the following expressions?
-#
-#
-# ```python
-# np.array(0) / np.array(0)
-# np.array(0) // np.array(0)
-# np.array([np.nan]).astype(int).astype(float)
-# ```
-#
-# #### 29. How to round away from zero a float array ? (★☆☆)
-#
-# (**hint**: np.uniform, np.copysign, np.ceil, np.abs)
-#
-#
-#
-# #### 30. How to find common values between two arrays? (★☆☆)
-#
-# (**hint**: np.intersect1d)
-#
-#
-#
-# #### 31. How to ignore all numpy warnings (not recommended)? (★☆☆)
-#
-# (**hint**: np.seterr, np.errstate)
-#
-#
-#
-# #### 32. Is the following expressions true? (★☆☆)
-#
-# (**hint**: imaginary number)
-#
-#
-# ```python
-# np.sqrt(-1) == np.emath.sqrt(-1)
-# ```
-#
-# #### 33. How to get the dates of yesterday, today and tomorrow? (★☆☆)
-#
-# (**hint**: np.datetime64, np.timedelta64)
-#
-#
-#
-# #### 34. How to get all the dates corresponding to the month of July 2016? (★★☆)
-#
-# (**hint**: np.arange(dtype=datetime64\['D'\]))
-#
-#
-#
-# #### 35. How to compute ((A+B)\*(-A/2)) in place (without copy)? (★★☆)
-#
-# (**hint**: np.add(out=), np.negative(out=), np.multiply(out=), np.divide(out=))
-#
-#
-#
-# #### 36. Extract the integer part of a random array using 5 different methods (★★☆)
-#
-# (**hint**: %, np.floor, np.ceil, astype, np.trunc)
-#
-#
-#
-# #### 37. Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)
-#
-# (**hint**: np.arange)
-#
-#
-#
-# #### 38. Consider a generator function that generates 10 integers and use it to build an array (★☆☆)
-#
-# (**hint**: np.fromiter)
-#
-#
-#
-# #### 39. Create a vector of size 10 with values ranging from 0 to 1, both excluded (★★☆)
-#
-# (**hint**: np.linspace)
-#
-#
-#
-# #### 40. Create a random vector of size 10 and sort it (★★☆)
-#
-# (**hint**: sort)
-#
-#
-#
-# #### 41. How to sum a small array faster than np.sum? (★★☆)
-#
-# (**hint**: np.add.reduce)
-#
-#
-#
-# #### 42. Consider two random array A and B, check if they are equal (★★☆)
-#
-# (**hint**: np.allclose, np.array\_equal)
-#
-#
-#
-# #### 43. Make an array immutable (read-only) (★★☆)
-#
-# (**hint**: flags.writeable)
-#
-#
-#
-# #### 44. Consider a random 10x2 matrix representing cartesian coordinates, convert them to polar coordinates (★★☆)
-#
-# (**hint**: np.sqrt, np.arctan2)
-#
-#
-#
-# #### 45. Create random vector of size 10 and replace the maximum value by 0 (★★☆)
-#
-# (**hint**: argmax)
-#
-#
-#
-# #### 46. Create a structured array with `x` and `y` coordinates covering the \[0,1\]x\[0,1\] area (★★☆)
-#
-# (**hint**: np.meshgrid)
-#
-#
-#
-# ####  47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
-#
-# #####  (hint: np.subtract.outer)
-#
-#
-#
-# #### 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)
-#
-# (**hint**: np.iinfo, np.finfo, eps)
-#
-#
-#
-# #### 49. How to print all the values of an array? (★★☆)
-#
-# (**hint**: np.set\_printoptions)
-#
-#
-#
-# #### 50. How to find the closest value (to a given scalar) in a vector? (★★☆)
-#
-# (**hint**: argmin)
-#
-#
-#
-# #### 51. Create a structured array representing a position (x,y) and a color (r,g,b) (★★☆)
-#
-# (**hint**: dtype)
-#
-#
-#
-# #### 52. Consider a random vector with shape (100,2) representing coordinates, find point by point distances (★★☆)
-#
-# (**hint**: np.atleast\_2d, T, np.sqrt)
-#
-#
-#
-# #### 53. How to convert a float (32 bits) array into an integer (32 bits) in place?
-#
-# (**hint**: astype(copy=False))
-#
-#
-#
-# #### 54. How to read the following file? (★★☆)
-#
-# (**hint**: np.genfromtxt)
-#
-#
-# ```
-# 1, 2, 3, 4, 5
-# 6,  ,  , 7, 8
-#  ,  , 9,10,11
-# ```
-#
-# #### 55. What is the equivalent of enumerate for numpy arrays? (★★☆)
-#
-# (**hint**: np.ndenumerate, np.ndindex)
-#
-#
-#
-# #### 56. Generate a generic 2D Gaussian-like array (★★☆)
-#
-# (**hint**: np.meshgrid, np.exp)
-#
-#
-#
-# #### 57. How to randomly place p elements in a 2D array? (★★☆)
-#
-# (**hint**: np.put, np.random.choice)
-#
-#
-#
-# #### 58. Subtract the mean of each row of a matrix (★★☆)
-#
-# (**hint**: mean(axis=,keepdims=))
-#
-#
-#
-# #### 59. How to sort an array by the nth column? (★★☆)
-#
-# (**hint**: argsort)
-#
-#
-#
-# #### 60. How to tell if a given 2D array has null columns? (★★☆)
-#
-# (**hint**: any, ~)
-#
-#
-#
-# #### 61. Find the nearest value from a given value in an array (★★☆)
-#
-# (**hint**: np.abs, argmin, flat)
-#
-#
-#
-# #### 62. Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? (★★☆)
-#
-# (**hint**: np.nditer)
-#
-#
-#
-# #### 63. Create an array class that has a name attribute (★★☆)
-#
-# (**hint**: class method)
-#
-#
-#
-# #### 64. Consider a given vector, how to add 1 to each element indexed by a second vector (be careful with repeated indices)? (★★★)
-#
-# (**hint**: np.bincount | np.add.at)
-#
-#
-#
-# #### 65. How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)
-#
-# (**hint**: np.bincount)
-#
-#
-#
-# #### 66. Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique colors (★★★)
-#
-# (**hint**: np.unique)
-#
-#
-#
-# #### 67. Considering a four dimensions array, how to get sum over the last two axis at once? (★★★)
-#
-# (**hint**: sum(axis=(-2,-1)))
-#
-#
-#
-# #### 68. Considering a one-dimensional vector D, how to compute means of subsets of D using a vector S of same size describing subset  indices? (★★★)
-#
-# (**hint**: np.bincount)
-#
-#
-#
-# #### 69. How to get the diagonal of a dot product? (★★★)
-#
-# (**hint**: np.diag)
-#
-#
-#
-# #### 70. Consider the vector \[1, 2, 3, 4, 5\], how to build a new vector with 3 consecutive zeros interleaved between each value? (★★★)
-#
-# (**hint**: array\[::4\])
-#
-#
-#
-# #### 71. Consider an array of dimension (5,5,3), how to mulitply it by an array with dimensions (5,5)? (★★★)
-#
-# (**hint**: array\[:, :, None\])
-#
-#
-#
-# #### 72. How to swap two rows of an array? (★★★)
-#
-# (**hint**: array\[\[\]\] = array\[\[\]\])
-#
-#
-#
-# #### 73. Consider a set of 10 triplets describing 10 triangles (with shared vertices), find the set of unique line segments composing all the  triangles (★★★)
-#
-# (**hint**: repeat, np.roll, np.sort, view, np.unique)
-#
-#
-#
-# #### 74. Given an array C that is a bincount, how to produce an array A such that np.bincount(A) == C? (★★★)
-#
-# (**hint**: np.repeat)
-#
-#
-#
-# #### 75. How to compute averages using a sliding window over an array? (★★★)
-#
-# (**hint**: np.cumsum)
-#
-#
-#
-# #### 76. Consider a one-dimensional array Z, build a two-dimensional array whose first row is (Z\[0\],Z\[1\],Z\[2\]) and each subsequent row is  shifted by 1 (last row should be (Z\[-3\],Z\[-2\],Z\[-1\]) (★★★)
-#
-# (**hint**: from numpy.lib import stride\_tricks)
-#
-#
-#
-# #### 77. How to negate a boolean, or to change the sign of a float inplace? (★★★)
-#
-# (**hint**: np.logical_not, np.negative)
-#
-#
-#
-# #### 78. Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to compute distance from p to each line i  (P0\[i\],P1\[i\])? (★★★)
-#
-#
-#
-# #### 79. Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P, how to compute distance from each point j (P\[j\]) to each line i (P0\[i\],P1\[i\])? (★★★)
-#
-#
-#
-# #### 80. Consider an arbitrary array, write a function that extract a subpart with a fixed shape and centered on a given element (pad with a `fill` value when necessary) (★★★)
-#
-# (**hint**: minimum, maximum)
-#
-#
-#
-# #### 81. Consider an array Z = \[1,2,3,4,5,6,7,8,9,10,11,12,13,14\], how to generate an array R = \[\[1,2,3,4\], \[2,3,4,5\], \[3,4,5,6\], ..., \[11,12,13,14\]\]? (★★★)
-#
-# (**hint**: stride\_tricks.as\_strided)
-#
-#
-#
-# #### 82. Compute a matrix rank (★★★)
-#
-# (**hint**: np.linalg.svd)
-#
-#
-#
-# #### 83. How to find the most frequent value in an array?
-#
-# (**hint**: np.bincount, argmax)
-#
-#
-#
-# #### 84. Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)
-#
-# (**hint**: stride\_tricks.as\_strided)
-#
-#
-#
-# #### 85. Create a 2D array subclass such that Z\[i,j\] == Z\[j,i\] (★★★)
-#
-# (**hint**: class method)
-#
-#
-#
-# #### 86. Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1). How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)
-#
-# (**hint**: np.tensordot)
-#
-#
-#
-# #### 87. Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)
-#
-# (**hint**: np.add.reduceat)
-#
-#
-#
-# #### 88. How to implement the Game of Life using numpy arrays? (★★★)
-#
-#
-#
-# #### 89. How to get the n largest values of an array (★★★)
-#
-# (**hint**: np.argsort | np.argpartition)
-#
-#
-#
-# #### 90. Given an arbitrary number of vectors, build the cartesian product (every combinations of every item) (★★★)
-#
-# (**hint**: np.indices)
-#
-#
-#
-# #### 91. How to create a record array from a regular array? (★★★)
-#
-# (**hint**: np.core.records.fromarrays)
-#
-#
-#
-# #### 92. Consider a large vector Z, compute Z to the power of 3 using 3 different methods (★★★)
-#
-# (**hint**: np.power, \*, np.einsum)
-#
-#
-#
-# #### 93. Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A that contain elements of each row of B regardless of the order of the elements in B? (★★★)
-#
-# (**hint**: np.where)
-#
-#
-#
-# #### 94. Considering a 10x3 matrix, extract rows with unequal values (e.g. \[2,2,3\]) (★★★)
-#
-#
-#
-# #### 95. Convert a vector of ints into a matrix binary representation (★★★)
-#
-# (**hint**: np.unpackbits)
-#
-#
-#
-# #### 96. Given a two dimensional array, how to extract unique rows? (★★★)
-#
-# (**hint**: np.ascontiguousarray | np.unique)
-#
-#
-#
-# #### 97. Considering 2 vectors A & B, write the einsum equivalent of inner, outer, sum, and mul function (★★★)
-#
-# (**hint**: np.einsum)
-#
-#
-#
-# #### 98. Considering a path described by two vectors (X,Y), how to sample it using equidistant samples (★★★)?
-#
-# (**hint**: np.cumsum, np.interp)
-#
-#
-#
-# #### 99. Given an integer n and a 2D array X, select from X the rows which can be interpreted as draws from a multinomial distribution with n degrees, i.e., the rows which only contain integers and which sum to n. (★★★)
-#
-# (**hint**: np.logical\_and.reduce, np.mod)
-#
-#
-#
-# #### 100. Compute bootstrapped 95% confidence intervals for the mean of a 1D array X (i.e., resample the elements of an array with replacement N times, compute the mean of each sample, and then compute percentiles over the means). (★★★)
-#
-# (**hint**: np.percentile)
-#