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:
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Input: n = 2, trust = [[1,2]]
Output: 2
Example 2:
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Input: n = 3, trust = [[1,3],[2,3]]
Output: 3
Example 3:
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Input: n = 3, trust = [[1,3],[2,3],[3,1]]
Output: -1
Example 4:
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Input: n = 3, trust = [[1,2],[2,3]]
Output: -1
Example 5:
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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;
}
};