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
Solution
根据题意，作为一个法官，如果有N个人，那么必须要有N-1个人信任他，也就是在trust列表的第二个元素个数要等于N-1，而且，他不相信任何人，也就是说他不会出现在trust列表的第一个元素上。用个图形来表示，下图中1，2，4都信任3，而3不信任任何人，也就是入度-出度= N-1
class Solution:
def findJudge(self, N: int, trust: List[List[int]]) -> int:
ct= [0] * (N+1)
for x, y in trust:
ct[x] -=1
ct[y] +=1
for i in range(1,N+1):
if ct[i] ==N-1:
return i
return -1
