'''
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


Constraints:

1 <= N <= 1000
0 <= trust.length <= 10^4
trust[i].length == 2
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:
        if N == 1:
            if trust:
                return -1
            else:
                return 1
        in_degree = [0 for i in range(N + 1)]
        out_degree = [0 for i in range(N + 1)]
        for pair in trust:
            out_degree[pair[0]] += 1
            in_degree[pair[1]] += 1
        for n in range(N + 1):
            if in_degree[n] == N - 1 and out_degree[n] == 0:
                return n
        return -1