Find the Town Judge

class Solution:
    def findJudge(self, n: int, trust: List[List[int]]) -> int:
        out = Counter(ele[0] for ele in trust)
        inc = Counter(ele[1] for ele in trust)
        for i in range(1, n+1):
            if out[i] == 0 and inc[i] == n-1:
                return i
        return -1

#using one hashtable
'''
"""
Why mp[i] == n-1 works?
Our goal is to find a node which has 0 outgoing edges and n-1 incoming edges.(at most there can be only one such node)
So in mp[i] we are storing the count of incoming edges in excess to the outgoing edges.
So mp[i] == n-1 means that for node i there are n-1 more incoming edges than outgoing ones, but we know that at any particular node there cannot be more than n-1 total edges (incoming + outgoing), so in this case outgoing edges has to be zero and incoming edges n-1, which is the judge condition.
By the same reasoning all non-judge nodes will have values less than n-1(either due to shortage of incoming edges or presence of outgoing edge)
"""
class Solution:
    def findJudge(self, n: int, trust: List[List[int]]) -> int:
        mp = Counter()
        for a, b in trust:
            mp[b] += 1
            mp[a] -= 1

        for i in range(1, n+1):
            if mp[i] == n-1:
                return i
        return -1

'''