997. Find the Town Judge

Problem Link

Description

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

Solution

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Python3

class Solution:
    def findJudge(self, n: int, trust: List[List[int]]) -> int:
        trusted = [0] * (n + 1)
        trust_other = [0] * (n + 1)
        
        for u, v in trust:
            trusted[v] += 1
            trust_other[u] += 1
        
        for i in range(1, n + 1):
            if trusted[i] == n - 1 and trust_other[i] == 0:
                return i
        
        return -1