hdu 1521 记忆化搜索

应该说，就是道DP题，最近用记忆化搜索用得老爽了，就用了~

/*
 * hdu1521/win.cpp
 * Created on: 2011-10-3
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;

const int MAXN = 12;
const int fac[] = { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800 };
int num[MAXN], sum[MAXN];
int dp[MAXN][MAXN];

int search(int n, int m) {
    if (dp[n][m] >= 0) {
        return dp[n][m];
    }
    if (sum[n] < m) {
        dp[n][m] = 0;
        return 0;
    }
    long long ret = 0;
    for (int i = 0; i <= m && i <= num[n]; i++) {
        ret += (long long) search(n - 1, m - i) * fac[m] / fac[m - i] / fac[i];
    }
    dp[n][m] = ret;
    return ret;
}

void init(int n) {
    for (int i = 1; i <= n; i++) {
        scanf("%d", &num[i]);
    }
    memset(dp, -1, sizeof(dp));
    for (int i = 0; i <= n; i++) {
        dp[i][0] = 1;
    }
    sum[0] = 0;
    for (int i = 1; i <= n; i++) {
        sum[i] = sum[i - 1] + num[i];
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int n, m;
    while (scanf("%d%d", &n, &m) == 2) {
        init(n);
        printf("%d\n", search(n, m));
    }
    return 0;
}