ONE_ZERO SPOJ 

http://www.spoj.com/problems/ONEZERO/

It's very important to make a visited array [1...n], so that the number which is visited once will not be visited again, if we would not make this visited it will definitely lead to TLE :P (idea credit kishlay )

solution

#include<bits/stdc++.h>

using namespace std;

string bfs(int n)

{

 pair<int,string> temp;

 queue<pair<int,string> > st;

 st.push(make_pair(1,"1"));

 int visited[n];

 for(int i=0;i<n;i++) visited[i]=0; visited[1]=1;

 while(!st.empty())

 {

  string tt1,tt2;

  temp=st.front();

  st.pop();

  if(temp.first%n!=0)

  {

    tt1=temp.second+"0";

    //cout<<tt<<" ";

    if(visited[(temp.first*10)%n]==0){

    st.push(make_pair((temp.first*10)%n,tt1));

    visited[(temp.first*10)%n]=1;}

     tt2=temp.second+"1";

    if(visited[(temp.first*10+1)%n]==0){

    st.push(make_pair((temp.first*10+1)%n,tt2));

    visited[(temp.first*10+1)%n]=1;}

  }

  else

  {

    return temp.second;

  }

 }

}

int main()

{

 int t;

 cin>>t;

 while(t--)

 {

  int n;

  cin>>n;

  string pp=bfs(n);

  cout<<pp<<endl;

 }

return 0;

}