# Find The Town Judge Problem

## Description

LeetCode Problem 997.

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:

• 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 an array trust where trust[i] = [a_i, b_i] representing that the person labeled a_i trusts the person labeled b_i.

Return the label of the town judge if the town judge exists and can be identified, or return -1 otherwise.

Example 1:

``````1
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Input: n = 2, trust = [[1,2]]
Output: 2
``````

Example 2:

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

Example 3:

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

Example 4:

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

Example 5:

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

Constraints:

• 1 <= n <= 1000
• 0 <= trust.length <= 10^4
• trust[i].length == 2
• All the pairs of trust are unique.
• a_i != b_i
• 1 <= a_i, b_i <= n

## Sample C++ Code

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class Solution {
public:
int findJudge(int N, vector<vector<int>>& trust) {
unordered_map<int, int> m;
for (int i = 1; i <= N; i ++)
m[i] = 0;
for (int i = 0; i < trust.size(); i ++) {
m[trust[i][0]] --;
m[trust[i][1]] ++;
}
for (int i = 1; i <= N; i ++) {
if (m[i] == N-1)
return i;
}
return -1;
}
};
``````