HDU 1521 search permutations

Permutations

Problem Description

There are n kinds of goods, and know the number of each item. Required number of permutations of m selected items therefrom. For example, there are two items A, B, and the number is 1, 2 from the selected items are arranged the "AB", "BA" two kinds.

 

 

Input

Each group has two data input lines, the first line is two numbers n, m (1 <= m, n <= 10), indicates the number of items, the second row has the number n, the n denote the number of items .

 

 

Output

Each number corresponding to a data output arrangement. (Any operation are not exceeded 2 ^ 31)

 

 

Sample Input

2 2 1 1

 

 

Sample Output

2

 AC Code

#include<bits/stdc++.h>
using namespace std;
int n,m,s,a[11];
void dfs(int x){
    if(x==0){
        s++;return;
    }
    for(int i=0;i<n;++i){
        if(a[i]){
            a[i]--;
            dfs(x-1);
            a[i]++;
        }
    }
}
int main(){
    while(cin>>n>>m)
    {
        s=0;
        for(int i=0;i<n;i++)
        {
            scanf("%d",&a[i]);
        }
        dfs(m);
        cout<<s<<endl;
    }
    return 0;
}

dfs If only find the solution does not require backtracking

If you need to find all the solutions you need