Find the Town Judge.cpp

/*
Find the Town Judge
Solution
In a town, there are N people labelled from 1 to N.  There is a rumor that one of these people is secretly the town judge.

If the town judge exists, then:

The town judge trusts nobody.
Everybody (except for the town judge) trusts the town judge.
There is exactly one person that satisfies properties 1 and 2.
You are given trust, an array of pairs trust[i] = [a, b] representing that the person labelled a trusts the person labelled b.

If the town judge exists and can be identified, return the label of the town judge.  Otherwise, return -1.

 

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
Example 4:

Input: N = 3, trust = [[1,2],[2,3]]
Output: -1
Example 5:

Input: N = 4, trust = [[1,3],[1,4],[2,3],[2,4],[4,3]]
Output: 3
 

Note:

1 <= N <= 1000
trust.length <= 10000
trust[i] are all different
trust[i][0] != trust[i][1]
1 <= trust[i][0], trust[i][1] <= N

Submission Detail
89 / 89 test cases passed.
Status: Accepted
Runtime: 500 ms
Memory Usage: 62.5 MB
*/
class Solution {
public:
    int findJudge(int N, vector<vector<int>>& trust) {
        map<int,int> n,m;
        if(N == 1)
        {
            return N;
        }
        for(int i=0;i<trust.size();i++)
        {
            n[trust[i][0]] = n[trust[i][0]] + 1;
            m[trust[i][1]] = m[trust[i][1]] + 1;
        }
        for(auto p : m)
        {
            if(p.second == N-1 && n[p.first]==NULL)
            {
                return p.first;
            }
        }
        return -1;
    }
};