find the guy every one know

There are N people in the town (N>=2), and function Know(i,j) return true if i knows j and false otherwise. The knowing relationship is not symmetric. Know(i,j)==true cannot guarantee Know(j,i)==true. Find those people: everyone knows him but he knows nobody else.
 

int find()
{
    int i =0;
    int j =1;
    int next =2;
    //first find the gay
while(next <= N)     //if still have someone not remove
    {
        if (Know(i, j))     //if i know j, i is not we want
        {
            i = next;
        }
        else
        {
            j = next;
        }
        ++next; //consider the next one
    }
    int cand = i;    //candidate
if (i == N)
    {
        cand = j;
    }
    //check if the cadidate is the one we want to find
for (int k =0; k < N; ++k)
    {
        if (k == cond)
        {
            continue;
        }
        if (Know(cand, k) ||!Know(k, cand))     //if candidate know k or k not know candidate
        {
            return-1;
        }
    }
    return cand;
}