0997-Find-the-Town-Judge.py

'''
In a town, there are N people labelled 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 trust, an array of pairs trust[i] = [a, b] representing that the person labelled a trusts the person labelled b.

If the town judge exists and can be identified, return the label of the town judge.  Otherwise, return -1.



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

Example 4:

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

Example 5:

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



Note:

    1 <= N <= 1000
    trust.length <= 10000
    trust[i] are all different
    trust[i][0] != trust[i][1]
    1 <= trust[i][0], trust[i][1] <= N
'''
class Solution:
    def findJudge(self, N: int, trust: List[List[int]]) -> int:
        degree = [0] * (N + 1)
        for i, j in trust:
            degree[i] -= 1
            degree[j] += 1
        for i in range(1, N + 1):
            if degree[i] == N - 1:
                return i
        return -1