Leetcode 1039 Solution

This article provides solution to leetcode question 1039 (find-the-town-judge)
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https://leetcode.com/problems/find-the-town-judge

Solution

class Solution:
    def findJudge(self, N: int, trust: List[List[int]]) -> int:
        m = collections.defaultdict(set)
        for s, d in trust:
            m[s].add(d)

        judge = None
        for i in range(1, N + 1):
            if not m[i]:
                if not judge:
                    judge = i
                else:
                    return -1

        for i in range(1, N + 1):
            if i == judge:
                continue
            if judge not in m[i]:
                return -1

        return judge