Project Euler Problem 24

问题：

A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we call it lexicographic order. The lexicographic permutations of 0, 1 and 2 are:

012   021   102   120   201   210

What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?

答案：2783915460

#include

int N(int n)
{
    int sum = 1;
    int i = 1;

    for (i=1; i<=n; i++)
        sum *= i;

    return sum;
}

int main(void)
{
    int a = 999999;
    int r[9] = {0};
    int s[10] = {0};
    int t = 0;

    int i = 9;

    for (i=0; i<10; i++)
        s[i] = i;

    for (i=9; i>0; i--){
        t = N(i);
        r[9-i] = a / t;
        a = a % t;
        //printf("%d ", r[9-i]);
    }

    putchar('\n');

    int j = 0, k = 0;
    for (i=0; i<9; i++)
    {
        for (j=0, k=0; k            if (s[j] == -1)
                continue;
            else
                k++;

        for (; j<10; j++)
            if(s[j] != -1){
                printf("%d", s[j]);
                s[j] = -1;
                break;
            }
    }

    for (i=0; i<10; i++)
        if (s[i] == -1)
            continue;
        else
            printf("%d", s[i]);


    return 0;
}