hdu 1521 排列组合 指数型母函数

 

/*
 * hdu1521.c
 *
 *  Created on: 2011-8-31
 *      Author: 王竹
 */

#include<stdio.h>
#include<string.h>
#define nmax 15
int num[nmax];
double res[nmax], fac[nmax], temp[nmax];
void init(int n) {
    int i;
    fac[0] = 1;
    for (i = 1; i <= n; i++) {
        fac[i] = fac[i - 1] * i;
    }
}
int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int i, j, k, n, m;
    while (scanf("%d %d", &n, &m) != EOF) {
        init(n);
        for (i = 0; i < n; i++) {
            scanf("%d", num + i);
        }
        memset(res, 0.0, sizeof(res));
        memset(temp, 0.0, sizeof(res));
        for (i = 0; i <= num[0]; i++) {
            res[i] = 1.0 / fac[i];
        }
        for (i = 1; i < n; i++) {
            for (j = 0; j <= n; j++) {
                for (k = 0; (k <= num[i]) && (k + j <= n); k++) {
                    temp[j + k] += res[j] / fac[k];
                }
            }
            for (j = 0; j <= n; j++) {
                res[j] = temp[j], temp[j] = 0;
            }
        }
        printf("%.0lf\n", res[m] * fac[m]);
    }
    return 0;
}