ProjectEuler/c/0008.c

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>

#include "da.h"


DA_DEF_STRUCT(char, str);
DA_DEF_STRUCT(uint64_t, prods);

void str_append(struct str *str, const char *cstr);
uint8_t char_to_u8(char c);

int
main(int argc, const char **argv)
{
	uint64_t res = 0;
	uint64_t i = 0, j = 0;
	uint64_t window_size = 13;
	struct str str = {NULL, 0, 1024};
	struct prods prods = {0};
	DA_CREATE(prods, sizeof(*prods.items));

	str.items = calloc(str.cap, sizeof(*str.items));

	str_append(&str, "73167176531330624919225119674426574742355349194934");
	str_append(&str, "96983520312774506326239578318016984801869478851843");
	str_append(&str, "85861560789112949495459501737958331952853208805511");
	str_append(&str, "12540698747158523863050715693290963295227443043557");
	str_append(&str, "66896648950445244523161731856403098711121722383113");
	str_append(&str, "62229893423380308135336276614282806444486645238749");
	str_append(&str, "30358907296290491560440772390713810515859307960866");
	str_append(&str, "70172427121883998797908792274921901699720888093776");
	str_append(&str, "65727333001053367881220235421809751254540594752243");
	str_append(&str, "52584907711670556013604839586446706324415722155397");
	str_append(&str, "53697817977846174064955149290862569321978468622482");
	str_append(&str, "83972241375657056057490261407972968652414535100474");
	str_append(&str, "82166370484403199890008895243450658541227588666881");
	str_append(&str, "16427171479924442928230863465674813919123162824586");
	str_append(&str, "17866458359124566529476545682848912883142607690042");
	str_append(&str, "24219022671055626321111109370544217506941658960408");
	str_append(&str, "07198403850962455444362981230987879927244284909188");
	str_append(&str, "84580156166097919133875499200524063689912560717606");
	str_append(&str, "05886116467109405077541002256983155200055935729725");
	str_append(&str, "71636269561882670428252483600823257530420752963450");

	for ( i = 0; i < str.size - window_size; ++i ) {
		uint64_t t = 1;
		for ( j = 0; j < window_size; ++j ) {
			t *= (uint64_t) char_to_u8(*(str.items + i + j));
		}
		DA_APPEND(prods, t);
	}

	for ( i = 0; i < prods.size; ++i ) {
		if ( prods.items[i] > res ) {
			res = prods.items[i];
		}
	}

	printf("Result = %ld!\n", res);
	free(str.items);
	free(prods.items);
	(void) argc; (void) argv;
	return 0;
}

void
str_append(struct str *str, const char *cstr)
{
	uint64_t cstr_lenght = strlen(cstr);
	if ( (str->size + cstr_lenght) >= str->cap ) {
		str->cap *= 2;
		str->items = realloc(str->items, str->cap);
	}

	while ( *cstr != '\0' ) {
		str->items[str->size++] = *cstr;
		++cstr;
	}
}

uint8_t
char_to_u8(char c)
{
	return (uint8_t)(c - '0');
}