有个问题，求指教编写思路-_-||

n*(n-1)*(n-2).....*1

#include<iostream>
#include<algorithm>
#include<math.h>
using namespace std;
void main(){
int m,n,a[100],i;
cout<<"输入n和m:"<<endl;
cin>>n>>m;
for(i=0;i<n;i++){
cin>>a[i];
}
do{
copy(a,a+m,ostream_iterator<int>(cout,""));
cout<<endl;
}while(next_permutation(a,a+n));
}