997 Find the Town Judge.py

Author: rajeevranjancom

997 Find the Town Judge.py

@@ -0,0 +1,64 @@
+#!/usr/bin/python3
+"""
+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
+"""
+from typing import List
+from collections import defaultdict
+
+
+class Solution:
+    def findJudge(self, N: int, trust: List[List[int]]) -> int:
+        """
+        like the find the celebrity
+        """
+        ingress = defaultdict(set)
+        egress =defaultdict(set)
+        for p, q in trust:
+            egress[p].add(q)
+            ingress[q].add(p)
+        for i in range(1, N+1):
+            if len(egress[i]) == 0 and len(ingress[i]) == N - 1:
+                return i
+        return -1