/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
 *
 * Find the largest palindrome made from the product of two 3-digit numbers.*/

#define _POSIX_C_SOURCE 199309L

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "projecteuler.h"

int main(int argc, char **argv)
{
    int i, j, max = 0, num;
    double elapsed;
    struct timespec start, end;

    clock_gettime(CLOCK_MONOTONIC, &start);

    /* Using a brute-force approach: generate every product of 3-digit numbers
     * and check if it's palindrome. If the product found is greater than the
     * current maximum, save the current product.*/
    for(i = 999; i >= 100; i--)
    {
        for(j = i; j >= 100; j--)
        {
            num = i * j;
            /* Use the function defined in projecteuler.c to check if a number is palindrome.*/
            if(num > max && is_palindrome(num, 10))
            {
                max = num;
            }
        }
    }

    clock_gettime(CLOCK_MONOTONIC, &end);

    elapsed = (end.tv_sec - start.tv_sec) + (double)(end.tv_nsec - start.tv_nsec) / 1000000000;

    printf("Project Euler, Problem 4\n");
    printf("Answer: %d\n", max);

    printf("Elapsed time: %.9lf seconds\n", elapsed);

    return 0;
}