More pythonic

src/project_euler_python/create_template.py

@@ -22,7 +22,7 @@ def create_problem():
                                     https://projecteuler.net/problem={args["problem"]}
                                     """
 
-                                    from utils import timeit
+                                    from project_euler_python.utils import timeit
 
 
                                     @timeit("Problem {(args["problem"]):0>3}")

src/project_euler_python/problems_001_050/Problem008.py

@@ -9,8 +9,9 @@ Solution for problem 008 of Project Euler
 https://projecteuler.net/problem=8
 """
 
-import collections
+from collections import deque
 from itertools import islice
+from math import prod
 
 from project_euler_python.utils import timeit
 
@@ -19,7 +20,7 @@ from project_euler_python.utils import timeit
 def sliding_window(iterable, n):
     # sliding_window('ABCDEFG', 4) -> ABCD BCDE CDEF DEFG
     it = iter(iterable)
-    window = collections.deque(islice(it, n), maxlen=n)
+    window = deque(islice(it, n), maxlen=n)
     if len(window) == n:
         yield tuple(window)
     for x in it:
@@ -65,12 +66,10 @@ def compute():
     num = NUM.replace("\n", "").replace(" ", "")
     adjacent_digits = 13
     ans = 0
-    for nums in sliding_window(num, adjacent_digits):
+
-        prod = 1
+    for digits in sliding_window(num, adjacent_digits):
-        for num in nums:
+        window_product = prod(int(digit) for digit in digits)
-            prod *= int(num)
+        ans = max(ans, window_product)
-        if prod > ans:
-            ans = prod
 
     return ans
 

src/project_euler_python/problems_001_050/Problem009.py

@@ -24,9 +24,9 @@ def compute():
     Find the product abc.
     """
 
-    upper_limit = 1000
+    upper_limit = 1000 + 1
-    for a in range(1, upper_limit + 1):
+    for a in range(1, upper_limit):
-        for b in range(a + 1, upper_limit + 1):
+        for b in range(a + 1, upper_limit):
             c = upper_limit - a - b
             if a * a + b * b == c * c:
                 # It is now implied that b < c, because we have a > 0

src/project_euler_python/problems_001_050/Problem012.py

@@ -9,7 +9,7 @@ Solution for problem 012 of Project Euler
 https://projecteuler.net/problem=12
 """
 
-from itertools import count
+from itertools import accumulate, count
 from math import floor, sqrt
 
 from project_euler_python.utils import timeit
@@ -53,12 +53,10 @@ def compute():
     divisors?
     """
 
-    triangle = 0
+    limit = 500
-    for i in count(1):
+    for triangle in accumulate(count(1)):
-        # This is the ith triangle number, i.e. num = 1 + 2 + ... + i =
+        # This is the ith triangle number, i.e. num = 1 + 2 + ... + i = i*(i+1)/2
-        # = i*(i+1)/2
+        if num_divisors(triangle) > limit:
-        triangle += i
-        if num_divisors(triangle) > 500:
             return str(triangle)
 
 

src/project_euler_python/problems_001_050/Problem014.py

@@ -12,14 +12,14 @@ https://projecteuler.net/problem=14
 from project_euler_python.utils import timeit
 
 
-def chain_length(n, terms):
+def chain_length(n: int, terms: dict[int, int]) -> int:
     length = 0
     while n != 1:
         if n in terms:
             length += terms[n]
             break
         if n % 2 == 0:
-            n = n / 2
+            n //= 2
         else:
             n = 3 * n + 1
         length += 1
@@ -27,7 +27,7 @@ def chain_length(n, terms):
 
 
 @timeit("Problem 014")
-def compute():
+def compute() -> int:
     """
     The following iterative sequence is defined for the set of positive
     integers:
@@ -49,15 +49,17 @@ def compute():
     NOTE: Once the chain starts the terms are allowed to go above one million.
     """
 
-    ans = 0
     limit = 1_000_000
-    score = 0
+    ans = 0
-    terms = dict()
+    longest_length = 0
-    for i in range(1, limit):
+    chain_lengths = {1: 0}
-        terms[i] = chain_length(i, terms)
+
-        if terms[i] > score:
+    for start in range(2, limit):
-            score = terms[i]
+        current_length = chain_length(start, chain_lengths)
-            ans = i
+        chain_lengths[start] = current_length
+        if current_length > longest_length:
+            ans = start
+            longest_length = current_length
 
     return ans
 

src/project_euler_python/problems_001_050/Problem022.py

@@ -34,7 +34,7 @@ def compute():
         names = sorted(f.read().replace('"', "").split(","))
 
     ans = 0
-    for idx, name in enumerate(names, 1):
+    for idx, name in enumerate(names, start=1):
         ans += sum(ord(char) - 64 for char in name) * idx
 
     return ans

src/project_euler_python/problems_001_050/Problem023.py

@@ -9,9 +9,21 @@ Solution for problem 023 of Project Euler
 https://projecteuler.net/problem=23
 """
 
+from itertools import combinations_with_replacement
+
 from project_euler_python.utils import timeit
 
 
+def _get_abundant_numbers(limit):
+    divisor_sums = [0 for _ in range(limit)]
+
+    for divisor in range(1, limit):
+        for multiple in range(divisor * 2, limit, divisor):
+            divisor_sums[multiple] += divisor
+
+    return [number for number in range(1, limit) if divisor_sums[number] > number]
+
+
 @timeit("Problem 023")
 def compute():
     """
@@ -35,25 +47,19 @@ def compute():
     sum of two abundant numbers.
     """
 
-    limit = 28124
+    limit = 28123 + 1
-    divisor_sum = [0] * limit
+    abundant_numbers = _get_abundant_numbers(limit)
-    for i in range(1, limit):
-        for j in range(i * 2, limit, i):
-            divisor_sum[j] += i
 
-    abundant_nums = [i for (i, x) in enumerate(divisor_sum) if x > i]
+    expressible_sums = {
+        first + second
+        for first, second in combinations_with_replacement(
+            abundant_numbers,
+            2,
+        )
+        if first + second < limit
+    }
 
-    expressible = [False] * limit
+    return sum(number for number in range(1, limit) if number not in expressible_sums)
-    for i in abundant_nums:
-        for j in abundant_nums:
-            if i + j < limit:
-                expressible[i + j] = True
-            else:
-                break
-
-    ans = sum(i for (i, x) in enumerate(expressible) if not x)
-
-    return ans
 
 
 if __name__ == "__main__":

src/project_euler_python/problems_001_050/Problem024.py

@@ -9,7 +9,7 @@ Solution for problem 024 of Project Euler
 https://projecteuler.net/problem=24
 """
 
-from itertools import permutations
+from itertools import islice, permutations
 
 from project_euler_python.utils import timeit
 
@@ -28,9 +28,10 @@ def compute():
     0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?
     """
 
+    limit = 1_000_000
     digits = list(range(10))
-    _permutations = list(permutations(digits))
+    millionth_permutation = next(islice(permutations(digits), limit - 1, limit))
-    ans = "".join(str(digit) for digit in _permutations[999_999])
+    ans = "".join(str(digit) for digit in millionth_permutation)
 
     return ans
 

src/project_euler_python/problems_001_050/Problem026.py

@@ -37,11 +37,17 @@ def compute():
 
     cycle_length = 0
     ans = 0
+    # Because denominators with factor 2 contribute only to the terminating
+    # part of a decimal. The repeating behavior comes from the part of the
+    # denominator that is coprime with 10, so evens are skipped
     for number in range(3, 1000, 2):
         if number % 5 == 0:
             continue
         p = 1
-        while 10**p % number != 1:
+        remainder = 10 % number
+        while remainder != 1:
+            # avoid huge exponentiation
+            remainder = (remainder * 10) % number
             p += 1
         if p > cycle_length:
             cycle_length, ans = p, number

src/project_euler_python/problems_001_050/Problem032.py

@@ -29,11 +29,10 @@ def compute():
     """
 
     ans = set()
-    pandigital = ["1", "2", "3", "4", "5", "6", "7", "8", "9"]
+    pandigital = [str(number) for number in range(1, 10)]
 
     for x in range(1, 100):
         for y in range(100, 10_000):
-            # product = x * y
             if sorted(str(x) + str(y) + str(x * y)) == pandigital:
                 ans.add(x * y)
 

src/project_euler_python/problems_001_050/Problem036.py

@@ -9,11 +9,7 @@ Solution for problem 036 of Project Euler
 https://projecteuler.net/problem=36
 """
 
-from project_euler_python.utils import timeit
+from project_euler_python.utils import is_palindrome, timeit
-
-
-def is_palidrome(num):
-    return str(num) == str(num)[::-1]
 
 
 @timeit("Problem 036")
@@ -28,7 +24,7 @@ def compute():
 
     ans = 0
     for i in range(1, 1_000_001, 2):
-        if is_palidrome(i) and is_palidrome(bin(i)[2:]):
+        if is_palindrome(i) and is_palindrome(bin(i)[2:]):
             ans += i
 
     return ans

src/project_euler_python/problems_001_050/Problem041.py

@@ -12,14 +12,6 @@ https://projecteuler.net/problem=41
 from project_euler_python.utils import is_prime, timeit
 
 
-def is_pandigital(number):
-    number = sorted(str(number))
-    check = [str(i) for i in range(1, len(number) + 1)]
-    if number == check:
-        return True
-    return False
-
-
 @timeit("Problem 041")
 def compute():
     """
@@ -30,8 +22,10 @@ def compute():
     What is the largest n-digit pandigital prime that exists?
     """
 
+    pandigital = [str(number) for number in range(1, 10)]
+
     for ans in range(7654321, 1, -1):
-        if is_pandigital(ans):
+        if sorted(str(ans)) == pandigital[: len(str(ans))]:
             if is_prime(ans):
                 return ans
 

src/project_euler_python/problems_001_050/Problem043.py

@@ -36,7 +36,7 @@ def compute():
     """
 
     ans = []
-    pandigital = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
+    pandigital = [str(number) for number in range(1, 10)]
 
     for n in permutations(pandigital):
         n_ = "".join(n)