Find the Celebrity

 1 /* The knows API is defined in the parent class Relation.
 2       boolean knows(int a, int b); */
 3 
 4 public class Solution extends Relation {
 5     public int findCelebrity(int n) {
 6         int candidate = 0;
 7         for (int i = 1; i < n; i++) {
 8             if (knows(candidate, i)) {
 9                 candidate = i;
10             }
11         }
12         
13         for (int i = 0; i < n; i++) {
14             if (i != candidate && knows(candidate, i) || !knows(i, candidate)) {
15                 return -1;
16             }
17         }
18         return candidate;
19     }
20 }