Problem
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:
1. The town judge trusts nobody.
2. Everybody (except for the town judge) trusts the town judge.
3. 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
Solution
Two tables:
- one for counting how many trusts each person gets
- one for counting how many other people each person trusts
class Solution:
def findJudge(self, N: int, trust: List[List[int]]) -> int:
people = [0] * (N)
h = defaultdict(int)
for t in trust:
people[t[1]-1] += 1
h[t[0]-1] = 1
for i in range(N):
if people[i] >= N - 1 and h[i] == 0:
return i+1
return -1