uva 729 - The Hamming Distance Problem

#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
int n;
char str[1000];
cin>>n;
while(n--)
{
memset(str,0,sizeof(str));
int len,zero_num;
cin>>len>>zero_num;
for(int i=0; i<len-zero_num; i++)
str[i]='0';
for(int i=len-zero_num; i<len; i++)
str[i]='1';
str[len]='\0';
cout<<str<<endl;
while(next_permutation(str,str+len))
cout<<str<<endl;
if(n)cout<<endl;
}
return 0;
}