diff --git a/ipynb/Euler3.ipynb b/ipynb/Euler3.ipynb index 70a3d26..2c07562 100644 --- a/ipynb/Euler3.ipynb +++ b/ipynb/Euler3.ipynb @@ -15,17 +15,17 @@ " The prime factors of 13195 are 5, 7, 13 and 29.\n", " What is the largest prime factor of the number 600851475143?\n", "\n", - "I'll describe here how I think about this problem. There are two things to get right: the general plan of how to attack this problem, and the details of how to say it in Python.\n", + "I'll describe here how I think about this problem, at alevel suitable for a novice programmer. There are two things to get right: the general plan of how to attack this problem, and the details of how to say it in Python.\n", "\n", "## The General Plan\n", "\n", "I would like to be able to find the largest prime factor of *any* integer, not just 600851475143; I want `largest_prime_factor(n)`. Here's how I think about it:\n", "\n", - "- I don't know how to immediately find the largest prime factor of *n*. (How would I know which numbers are prime?)\n", + "- I don't know how to immediately find the *largest* prime factor of *n*. \n", "- I do know how to find the *smallest* prime factor: just go through the integers from 2 to *n*, in order. The first integer that evenly divides *n* must be the smallest prime factor. It is a factor because it evenly divides, it is smallest because we didn't find a smaller one first, and it is prime because if it were a composite number (like 4 or 9), then we would have found one of its factors (like 2 or 3) first.\n", "- Once I have the smallest prime factor ***p*** then I know: **the largest prime factor of *n* is the maximum of *p* and the largest prime factor of *n*/*p*.**\n", "- If *n* is prime, then the largest prime factor is *n*.\n", - "- If *n* is 1, then [by convention](https://oeis.org/wiki/Greatest_prime_factor_of_n) we say the greatest prime factor is 1, even though 1 is usually not considered a prime.\n" + "- If *n* is 1, then [by convention](https://oeis.org/wiki/Greatest_prime_factor_of_n) we say the largest prime factor is 1, even though 1 is usually not considered a prime." ] }, { @@ -53,7 +53,7 @@ }, { "cell_type": "code", - "execution_count": 1, + "execution_count": 10, "id": "249c7f13-cdf9-41a2-b0e7-8a3dec15f74b", "metadata": {}, "outputs": [], @@ -62,7 +62,7 @@ " \"\"\"The largest prime that evenly divides n.\n", " Find the smallest prime p that evenly divides n, \n", " and return the maximum of p and the largest prime factor of n/p.\n", - " For prime n and for 1, return n.\"\"\"\n", + " If n is prime or if n = 1, this will return n.\"\"\"\n", " for p in range(2, n):\n", " if n % p == 0: # n is composite\n", " return max(p, largest_prime_factor(n // p))\n", @@ -81,7 +81,7 @@ }, { "cell_type": "code", - "execution_count": 2, + "execution_count": 11, "id": "734de0e3-aafc-438a-8332-09741eef39aa", "metadata": {}, "outputs": [ @@ -91,7 +91,7 @@ "6857" ] }, - "execution_count": 2, + "execution_count": 11, "metadata": {}, "output_type": "execute_result" } @@ -142,7 +142,7 @@ }, { "cell_type": "code", - "execution_count": 3, + "execution_count": 12, "id": "9bedb1c9-4138-4250-90e6-77b10ba01586", "metadata": {}, "outputs": [ @@ -152,7 +152,7 @@ "'all tests pass'" ] }, - "execution_count": 3, + "execution_count": 12, "metadata": {}, "output_type": "execute_result" } @@ -167,6 +167,7 @@ " assert largest_prime_factor(36) == 3 # example from the diagram\n", " assert largest_prime_factor(49) == 7 # square of a prime\n", " assert largest_prime_factor(97) == 97 # bigger prime\n", + " assert largest_prime_factor(97 ** 9) == 97 # even bigger prime\n", " assert largest_prime_factor(600851475143) == 6857 # really big number\n", " return 'all tests pass'\n", "\n", @@ -185,7 +186,7 @@ }, { "cell_type": "code", - "execution_count": 4, + "execution_count": 13, "id": "0e4a1dc6-5969-49fd-9d65-11d9801cbea2", "metadata": {}, "outputs": [ @@ -193,8 +194,8 @@ "name": "stdout", "output_type": "stream", "text": [ - "CPU times: user 249 μs, sys: 20 μs, total: 269 μs\n", - "Wall time: 296 μs\n" + "CPU times: user 633 μs, sys: 71 μs, total: 704 μs\n", + "Wall time: 706 μs\n" ] }, { @@ -203,7 +204,7 @@ "6857" ] }, - "execution_count": 4, + "execution_count": 13, "metadata": {}, "output_type": "execute_result" } @@ -217,12 +218,12 @@ "id": "c8ead8e9-199f-47c6-ad76-360b1ebdaa02", "metadata": {}, "source": [ - "The algorithm should be slowest when *n* is prime, because then the `for` loop has to go all the way up to *n*. How long would it take for the largest 8-digit prime, 99,999,989?" + "The algorithm is slowest when *n* is prime, because the `for` loop has to go all the way up to *n*. How long would it take for the largest 8-digit prime, 99,999,989?" ] }, { "cell_type": "code", - "execution_count": 5, + "execution_count": 14, "id": "7323d528-96d7-4c05-a05d-125e99605443", "metadata": {}, "outputs": [ @@ -230,8 +231,8 @@ "name": "stdout", "output_type": "stream", "text": [ - "CPU times: user 1.92 s, sys: 6.64 ms, total: 1.93 s\n", - "Wall time: 1.93 s\n" + "CPU times: user 1.77 s, sys: 21.7 ms, total: 1.79 s\n", + "Wall time: 1.79 s\n" ] }, { @@ -240,7 +241,7 @@ "99999989" ] }, - "execution_count": 5, + "execution_count": 14, "metadata": {}, "output_type": "execute_result" } @@ -264,7 +265,7 @@ }, { "cell_type": "code", - "execution_count": 6, + "execution_count": 15, "id": "b90b5407-4666-4925-99d2-6a3a6b192fac", "metadata": {}, "outputs": [], @@ -275,7 +276,7 @@ " \"\"\"The largest prime that evenly divides n.\n", " Find the smallest prime p that evenly divides n, \n", " and return the maximum of p and the largest prime factor of n/p.\n", - " For prime n and for 1, return n.\"\"\"\n", + " If n is prime or if n = 1, this will return n.\"\"\"\n", " for p in range(2, int(sqrt(n) + 1)): # <<<< only need to go up to √n\n", " if n % p == 0: # n is composite\n", " return max(p, largest_prime_factor(n // p))\n", @@ -292,7 +293,7 @@ }, { "cell_type": "code", - "execution_count": 7, + "execution_count": 16, "id": "4026dc87-a0aa-4c75-b92a-96ec24cda1b7", "metadata": {}, "outputs": [ @@ -302,7 +303,7 @@ "'all tests pass'" ] }, - "execution_count": 7, + "execution_count": 16, "metadata": {}, "output_type": "execute_result" } @@ -321,7 +322,7 @@ }, { "cell_type": "code", - "execution_count": 8, + "execution_count": 17, "id": "d3d0c13e-5c01-4112-b372-60f7eb302d25", "metadata": {}, "outputs": [ @@ -329,8 +330,8 @@ "name": "stdout", "output_type": "stream", "text": [ - "CPU times: user 238 μs, sys: 1 μs, total: 239 μs\n", - "Wall time: 241 μs\n" + "CPU times: user 209 μs, sys: 0 ns, total: 209 μs\n", + "Wall time: 210 μs\n" ] }, { @@ -339,7 +340,7 @@ "99999989" ] }, - "execution_count": 8, + "execution_count": 17, "metadata": {}, "output_type": "execute_result" } @@ -353,14 +354,14 @@ "id": "82b008ea-f6b5-4bcd-8768-09c8dab089cb", "metadata": {}, "source": [ - "As advertised, this is about 10,000 times faster.\n", + "As predicted, this is about 10,000 times faster.\n", "\n", "We should be able to handle a 16-digit prime in about 2 seconds:" ] }, { "cell_type": "code", - "execution_count": 9, + "execution_count": 18, "id": "9b6030ef-626a-4195-aedb-ef2edac65da4", "metadata": {}, "outputs": [ @@ -368,8 +369,8 @@ "name": "stdout", "output_type": "stream", "text": [ - "CPU times: user 2.05 s, sys: 7.3 ms, total: 2.05 s\n", - "Wall time: 2.06 s\n" + "CPU times: user 2.15 s, sys: 22 ms, total: 2.17 s\n", + "Wall time: 2.17 s\n" ] }, { @@ -378,7 +379,7 @@ "9927935178558959" ] }, - "execution_count": 9, + "execution_count": 18, "metadata": {}, "output_type": "execute_result" } @@ -395,14 +396,14 @@ "source": [ "## Imperative versus Declarative (or Functional) Style\n", "\n", - "Our definition of largest_prime_factor mixed paradigms, using some imperative features (a for loop with a return in the middle) and some functional (an implementation of the equation `largest_prime_factor(n) = max(p, largest_prime_factor(n // p))`).\n", + "Our definition of largest_prime_factor mixed paradigms, using some [imperative](https://en.wikipedia.org/wiki/Imperative_programming) features (a for loop with a return in the middle) and some [functional](https://en.wikipedia.org/wiki/Functional_programming) features (an implementation of the equation `largest_prime_factor(n) = max(p, largest_prime_factor(n // p))`).\n", "\n", "Here's what it might look like if we leaned into the functional style more, making the equation more explicit:" ] }, { "cell_type": "code", - "execution_count": 10, + "execution_count": 19, "id": "0308612c-6860-49b0-bcd6-856fa08133b1", "metadata": {}, "outputs": [ @@ -412,7 +413,7 @@ "'all tests pass'" ] }, - "execution_count": 10, + "execution_count": 19, "metadata": {}, "output_type": "execute_result" } @@ -422,7 +423,7 @@ " \"\"\"The largest prime that evenly divides n.\n", " Find the smallest prime p that evenly divides n, \n", " and return the maximum of p and the largest prime factor of n/p.\n", - " For prime n and for 1, return n.\"\"\"\n", + " If n is prime or if n = 1, this will return n.\"\"\"\n", " p = smallest_prime_factor(n)\n", " return 1 if n == 1 else max(p, largest_prime_factor(n // p))\n", "\n", @@ -443,7 +444,7 @@ }, { "cell_type": "code", - "execution_count": 13, + "execution_count": 20, "id": "b8907a8f-872f-4531-825c-fae9c70211c1", "metadata": {}, "outputs": [ @@ -453,7 +454,7 @@ "'all tests pass'" ] }, - "execution_count": 13, + "execution_count": 20, "metadata": {}, "output_type": "execute_result" } @@ -463,7 +464,7 @@ " \"\"\"The largest prime that evenly divides n.\n", " Find the smallest prime p that evenly divides n, \n", " and return the maximum of p and the largest prime factor of n/p.\n", - " For prime n and for 1, return n.\"\"\"\n", + " If n is prime or if n = 1, this will return n.\"\"\"\n", " largest = 1\n", " p = 2\n", " while p * p <= n:\n", @@ -487,9 +488,9 @@ ], "metadata": { "kernelspec": { - "display_name": "Python [conda env:base] *", + "display_name": "Python 3 (ipykernel)", "language": "python", - "name": "conda-base-py" + "name": "python3" }, "language_info": { "codemirror_mode": {