/* It can be seen that the number, 125874, and its double, 251748, contain exactly the same digits, but in a different order.
 *
 * Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits.*/

#define _POSIX_C_SOURCE 199309L

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

int is_permutation(int a, int b);

int main(int argc, char **argv)
{
    int i;
    double elapsed;
    struct timespec start, end;

    clock_gettime(CLOCK_MONOTONIC, &start);

    i = 1;

    /* Brute force approach, try every integer number until the desired one is found.*/
    while(1)
    {
        if(is_permutation(i, 2*i) && is_permutation(i, 3*i) && is_permutation(i, 4*i) &&
                is_permutation(i, 5*i) && is_permutation(i, 6*i))
        {
            break;
        }

        i++;
    }

    clock_gettime(CLOCK_MONOTONIC, &end);

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

    printf("Project Euler, Problem 52\n");
    printf("Answer: %d\n", i);

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

    return 0;
}

int is_permutation(int a, int b)
{
    int i;
    int digits1[10] = {0}, digits2[10] = {0};

    /* Get digits of a.*/
    while(a > 0)
    {
        digits1[a%10]++;
        a /= 10;
    }

    /* Get digits of b.*/
    while(b > 0)
    {
        digits2[b%10]++;
        b /= 10;
    }

    /* If they're not the same, return 0.*/
    for(i = 0; i < 10; i++)
    {
        if(digits1[i] != digits2[i])
        {
            return 0;
        }
    }

    return 1;
}