[leetcode] 997. Find the Town Judge : https://leetcode.com/problems/find-the-town-judge/

Find the Town Judge.cpp

class Solution {
public:
    int findJudge(int N, vector<vector<int>>& trust) {
        vector<int> cnt(N+1, 0);
        for(int i=0;i<trust.size();i++){
            int from = trust[i][0];
            int to = trust[i][1];
            cnt[to]++; 
            cnt[from] = -N; // The town judge trusts nobody.
        }
        
        int answer = -1;
        for(int i=1;i<=N;i++){
            if(cnt[i] == N-1){ // Everybody (except for the town judge) trusts the town judge.
                if(answer == -1)
                    answer = i;
                else // There is exactly one person that satisfies properties 1 and 2.
                    return -1;
            }
        }
        return answer;
    }
};