http://www.spoj.pl/problems/PERMUT1/

permut1.c

#include <stdio.h>

int pd[13][99];

int permut(n, k) {

    if (pd[n][k] != -1)
        return pd[n][k];

    int i;
    pd[n][k] = 0;

    for (i = 0; i < n; i++){
        if(k - i < 0) break;
        pd[n][k] += permut(n - 1, k - i);
    }

    return pd[n][k];
}

int main(){

    int d, i, j, n, k;

    for (k = 0; k < 99; k++)
        pd[1][k] = 0;
    pd[1][0] = 1;

    for (n = 2; n < 13; n++) {
        for (k = 0; k < 99; k++) {
            pd[n][k] = -1;
        }
    } 

    scanf("%d", &d);

    for (i = 0; i < d; i++){
        scanf("%d %d", &n, &k);
        printf("%d\n", permut(n, k));
    }

    return 0;
}