[spoj][11574][A Famous Stone Collector]

题目：http://www.spoj.pl/problems/STONE2/

用生成函数的方法，其实也是dp的思想。

View Code

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;



const int mod = 1000000007;

const int N = 105;



#define M(a) ((a)%mod)

#define ll long long

ll ans, an[N], n, all;

ll t1[N*N], t2[N*N], c[N*N][N];



void init(){

    memset(c,0,sizeof(c));c[0][0]=1;

    for (int i=1; i<=10000; i++){

        c[i][0] = 1;

        for (int j=1; j<=min(i,100); j++)

            c[i][j] = M(c[i-1][j-1]+c[i-1][j]);

    }

}

int cas=1;

int main(){

    //freopen("D:/a.txt", "r", stdin);

    init();

    while (~scanf("%lld", &n)){

        all = ans = 0;

        memset(t1, 0, sizeof(t1));

        t1[0]=t2[0]=1;

        for (int i=1; i<=n; i++) scanf("%lld", &an[i]);

        for (int i=1; i<=n; i++){

            memset(t2,0,sizeof(t2));

            for (int j=0; j<=all; j++){

                for (int k=0; k<=an[i]; k++){

                    t2[k+j]=M(t2[k+j]+M(t1[j]*c[k+j][k]));

                }

            }

            all += an[i];

            for (int j=0; j<=all; j++)

                t1[j] = t2[j];

        }

        for (int i=1; i<=all; i++)

            ans = M(ans+t1[i]);

        printf("Case %d: %lld\n", cas++, ans);

    }

    return 0;

}