I didn't solve it by the easiest way..
This is my program, it gives right answers for my tests, but I have WA #3 , give me please this test

#include <cstdlib>
#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(int argc, char *argv[])
{
    long n,i,j,a;
    long na=65536;
    vector <long> pos,test;
    vector <long>:: iterator it;

    pos.push_back(1); pos.push_back(2);
    for (i=2;i<na;i++) { pos.push_back(pos[i-1]+i); }

    cin>>n;
    for (i=0;i<n;i++) { cin>>a; test.push_back(a); }

    sort(test.begin(),test.end());

    j=0;
    for (i=0;i<n;i++)
    {
        while ((j<na) && (test[i]>pos[j])) { j++; }
        if (j==na) { cout<<"0 "; }
        else if (test[i]==pos[j]) { cout<<"1 "; }
        else { cout<<"0 "; }
    }
    cout<<endl;

    system("PAUSE");
    return EXIT_SUCCESS;
}

Edited by author 05.05.2010 22:29

Have you tried for large values for k? It possibly overflows