Find the Town Judge | Leetcode Easy solution | leetcode 997

 997. Find the Town Judge

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.

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 <= 104
• trust[i].length == 2
• All the pairs of trust are unique.
• ai != bi
• 1 <= ai, bi <= n

Solution :

class Solution {

public:

    int findJudge(int n, vector<vector<int>>& trust) {

        unordered_map<int,int>indegree;

        unordered_map<int,int>outdegree;

        for(vector<int>x : trust)

        {

            int p = x[0];

            int q = x[1];

            indegree[q]++;

            outdegree[p]++;

        }

        for(int i = 1; i <= n ; i++)

        {

            if(indegree[i] == n-1 && outdegree[i] == 0)

                return i;

        }

        return -1;

    }

};