Add solution for problem-59 and a C solution for problem 40

problem-40.c

@@ -0,0 +1,65 @@
+#include<stdlib.h>
+#include<stdio.h>
+#include<string.h>
+
+#define MAX_NUM 1000000
+
+char* LETTERS = "0123456789";
+
+
+int digits(int* res, int num)
+{
+	int len = 0;
+	while (num > 0) {
+		len++;
+		res = (int*)realloc(res, len * sizeof(int));
+		res[len-1] = num % 10;
+		num /= 10;
+	}
+
+	return len;
+}
+
+
+int main(int argc, char** argv)
+{
+	char* str;
+	int* digs;
+	int nums, j, result;
+	int digit = 0, i = 0, num = 1;
+
+	str = malloc(MAX_NUM * sizeof(int));
+	digs = malloc(0 * sizeof(int));
+	nums = digits(digs, num);
+
+	while (digit < MAX_NUM) {
+		str[digit] = digs[nums-1-i];
+		digit++;
+		i++;
+		if (i == nums) {
+			/* refill digs and reset i */
+			num++;
+			nums = digits(digs, num);
+			i = 0;
+			/* DEBUG
+			printf("num = %d str = ", num);
+			for (j=0; j<digit; j++)
+				printf("%d", str[j]);
+			printf("\n");
+			*/
+		}
+	}
+
+	result = str[0] *
+		str[9] *
+		str[99] *
+		str[999] *
+		str[9999] *
+		str[99999] *
+		str[999999];
+
+	printf("The result is %d\n", result);
+	return 0;
+}
+
+

problem-59.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+import itertools
+import requests
+import string
+
+URL = "https://projecteuler.net/project/resources/p059_cipher.txt"
+
+def get_ciphertext(url):
+    resp = requests.get(url)
+    return resp.text
+
+
+def generate_keys(letters, length):
+    perms = itertools.permutations(letters, length)
+    yield from perms
+
+
+def ints_to_string(numbers):
+    return [chr(num) for num in numbers]
+
+
+def string_to_ints(letters):
+    return [ord(letter) for letter in letters]
+
+
+def xor_lists(xs, ys):
+    if len(xs) != len(ys):
+        raise Exception("Lists must be the same length")
+
+    return [a ^ b for a, b in zip(xs, ys)]
+
+
+def main():
+    text = get_ciphertext(URL)
+    cipher = [int(num) for num in text.split(',')]
+    letters = string.ascii_lowercase
+    common_words = ["the", "of", "to", "and", "in", "is", "it", "that"]
+    for perm in generate_keys(letters, 3):
+        key = "".join(list(perm))
+        cycled = string_to_ints(list(key * (len(cipher) // len(key))))
+        decrypt = "".join(ints_to_string(xor_lists(cipher, cycled)))
+        if all(word in decrypt for word in common_words):
+            print("Decrypted passage:")
+            print(decrypt)
+            print("Key: {0}".format(key))
+            print("Sum: {0}".format(sum(xor_lists(cipher, cycled))))
+
+
+if __name__ == "__main__":
+    main()