ProjectEuler/c/0004.c

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>

bool ispalindrome(const char *cstr, uint64_t cstr_size);

int
main(int argc, const char **argv)
{
	uint64_t res = 0;
	uint64_t sum = 0;
	uint64_t upper_limit = 999;
	uint64_t n1 = upper_limit, n2 = upper_limit;
	char str[16] = {0};
	uint64_t str_size = 0;

	while ( n2 > 0 ) {
		sum = n1 * n2;
		str_size = (uint64_t)sprintf(str, "%ld", sum);
		if ( ispalindrome(str, str_size) ) {
			if ( sum > res ) {
				res = sum;
			}
		}
		n1 -= ( n1 > 0 );
		if ( n1 == 0 ) {
			n1 = upper_limit;
			--n2;
		}
	}

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

bool
ispalindrome(const char *cstr, uint64_t cstr_size)
{
	uint64_t ptr_start = 0;
	uint64_t ptr_end = cstr_size-1;

	while ( ptr_start < ptr_end ) {
		if ( cstr[ptr_start] != cstr[ptr_end] ) {
			return false;
		}
		++ptr_start;
		--ptr_end;
	}
	return true;
}