997. Find the Town Judge

Easy

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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.

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

class Solution:
    def findJudge(self, n: int, trust: List[List[int]]) -> int:
        inDegree = [0]*n
        outDegree = [0]*n
        for a,b in trust:
            outDegree[a-1] += 1
            inDegree[b-1] += 1
        index = 0
        # print(inDegree)
        # print(outDegree)
        for degree in inDegree:
            if degree == (n-1):
                if outDegree[index] == 0:
                    return (index+1)
            index += 1
        return -1