277. Find the Celebrity.cpp

// Forward declaration of the knows API.
bool knows(int a, int b);

class Solution {
public:
    int findCelebrity(int n) {

        if (n <= 0)
            return n;

        int candidate = 0;

        for(int i = 1; i<n; ++i) {
            if (knows(candidate, i))
                candidate = i;
        }

        for(int i = 0;i<n; ++i) {

            if (i == candidate)
                continue;

            if (!knows(i, candidate) || knows(candidate, i))
                return -1;
        }

        return candidate;

    }
};