【HDOJ】1261 字串数

这道题目居然是大数。。。最开始审题，发现公式为(sum{A1...An})! / (A1!*A2*...AN!)。所以需要处理乘法大数，显然不会，看了一下别人的模板。

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <queue>
#include <algorithm>
#include <map>
#include <iomanip>
using namespace std;


#define INF 99999999
#define MAX 27

short s[MAX];
int sub[100];

void mult(int *sub,int sum,int m){
    int Base=10000, p=0;
    for (int i=1; i<=sub[0]; ++i){
        sub[i] = sub[i] * sum+p;
        p = sub[i] / Base;
        sub[i] = sub[i] % Base;
    }
    while (p){
        sub[0]++;
        sub[sub[0]] = p % Base;
        p = p / Base;
    }
    for(int i=sub[0]; i>=1; --i){
        sub[i] += p;
        p = (sub[i]%m) * Base;
        sub[i] = sub[i] / m;
    }
    while (!sub[sub[0]])
        sub[0]--;
}

void chg(int n,int m){
    for(int i=1; i<=m; ++i)
        mult(sub, n-m+i, i);//每次sub[]*(n-m+i)/i.
    return;
}

int main() {
    int n;

    while (cin >>n && n){
        int sum = 0;

        sub[0] = sub[1] = 1;
        for (int i=0; i<n; ++i){
            cin >>s[i];
            sum += s[i];
        }
        for (int i=0; i<n-1; ++i){
            chg(sum, s[i]);
            sum -=s [i];
        }
        cout <<sub[sub[0]];
        for (int i=sub[0]-1; i>=1; --i)
            cout<<setfill('0')<<setw(4)<<sub[i];

        cout<<endl;
    }

    return 0;
}