describe
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
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Example 2:
Input: N = 3, trust = [[1,3],[2,3]]
Output: 3
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Example 3:
Input: N = 3, trust = [[1, 3], [2, 3], [3, 1]] Output: 1Copy the code
Example 4:
Input: N = 3, trust = [[1,2],[2,3]]
Output: -1
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Example 5:
Input: N = 4, trust = [[1, 3], [1, 4], [2, 3], [2, 4], [4]] Output: 3Copy the code
Note:
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] <= NCopy the code
parsing
To find the hidden judge in the town, the judge must be satisfied that everyone else trusts him. So now we have a trust list that says A trusts B, so we can count everyone. Using a list D of length N+1 for everyone (the element with index 0 is useless, and the other indexes represent everyone in town), and then traversing each sub-list in trust [a,b], d[a]-=1 to indicate that he is definitely not a judge if he believes someone else, D [b]+=1 indicates that he is believed to be a judge. After traversal, as long as the count of the position in D is n-1, it indicates that it is a judge. Return its index, otherwise return -1.
answer
class Solution(object):
def findJudge(self, N, trust):
"""
:type N: int
:type trust: List[List[int]]
:rtype: int
"""
d = [0] * (N+1)
for a,b in trust:
d[a] -= 1
d[b] += 1
for person in range(1, N + 1):
if d[person] == N - 1:
return person
return -1
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The results
Given the submission in the Python online submissions. Memory Usage: 10000 ms The submissions in the Python online submissions for Find the Town Judge.Copy the code
Original link: leetcode.com/problems/fi…
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