Leetcode 277: Find the Celebrity (O(n))

leetcode_277b.cpp

#include <iostream>

using namespace std;

bool knows(int a, int b);

int findCelebrity(int n) {
    if (n==0) return -1;
    int celeb = 0;
    for (int i=1; i<n; ++i) {
        if (knows(celeb,i)) celeb=i;
    }

    for (int i=0; i<n; ++i) {
        if (i!=celeb && (knows(celeb,i) || !knows(i,celeb))) return -1;
    }
    return celeb;
}

//not runnable, requires leetcode knows() function