0053_P997_Find_the_Town_Judge.cpp

/* 
Day: 53
Problem Number: 997 (https://leetcode.com/problems/find-the-town-judge)
Date: 22-02-2024 
Description:
In a town, there are n people labeled from 1 to n. There is a rumor that one of these people is secretly the town judge.
If the town judge exists, then:
1. The town judge trusts nobody.
2. Everybody (except for the town judge) trusts the town judge.
3. There is exactly one person that satisfies properties 1 and 2.
You are given an array trust where trust[i] = [ai, bi] representing that the person labeled ai trusts the person labeled bi. If a trust relationship does not exist in trust array, then such a trust relationship does not exist.
Return the label of the town judge if the town judge exists and can be identified, or return -1 otherwise.
 
Example 1:
Input: n = 2, trust = [[1,2]]
Output: 2

Example 2:
Input: n = 3, trust = [[1,3],[2,3]]
Output: 3

Example 3:
Input: n = 3, trust = [[1,3],[2,3],[3,1]]
Output: -1

Constraints:
* 1 <= n <= 1000
* 0 <= trust.length <= 10^4
* trust[i].length == 2
* All the pairs of trust are unique.
* ai != bi
* 1 <= ai, bi <= n

Code:  */
class Solution {
public:
    int findJudge(int n, vector<vector<int>>& trust) {
        vector<int> cnt1(n + 1);
        vector<int> cnt2(n + 1);
        for (auto& t : trust) {
            int a = t[0], b = t[1];
            ++cnt1[a];
            ++cnt2[b];
        }
        for (int i = 1; i <= n; ++i) {
            if (cnt1[i] == 0 && cnt2[i] == n - 1) {
                return i;
            }
        }
        return -1;
    }
};