标签：count blog span note hashset input ida represent and
原题链接在这里：https://leetcode.com/problems/find-the-town-judge/
题目：
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:
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 <= 1000trust.length <= 10000trust[i] are all differenttrust[i][0] != trust[i][1]1 <= trust[i][0], trust[i][1] <= N题解：
Could find a candidate first with its trust set is empty.
Then iterate trust sets again to see if any other people‘s trust sets contains candidate, if not return -1.
Time Compleixty: O(N).
Space: O(N).
AC Java:
1 class Solution { 2 public int findJudge(int N, int[][] trust) { 3 if(N < 2){ 4 return N; 5 } 6 7 HashSet<Integer> [] trustSets = new HashSet[N+1]; 8 for(int i = 1; i<=N; i++){ 9 trustSets[i] = new HashSet<>(); 10 } 11 12 for(int [] t : trust){ 13 trustSets[t[0]].add(t[1]); 14 } 15 16 int c = -1; 17 for(int i = 1; i<=N; i++){ 18 if(trustSets[i].isEmpty()){ 19 c = i; 20 } 21 } 22 23 for(int i = 1; i<=N; i++){ 24 if(i != c && !trustSets[i].contains(c)){ 25 return -1; 26 } 27 } 28 29 return c; 30 } 31 }
We could count the trusts.
For each trust array t, t[0]--, t[1]++. And check if there is one count == N-1.
Time Complexity: O(N).
Space: O(N).
AC Java:
1 class Solution { 2 public int findJudge(int N, int[][] trust) { 3 if(N < 2){ 4 return N; 5 } 6 7 int [] count = new int[N+1]; 8 for(int [] t : trust){ 9 count[t[0]]--; 10 count[t[1]]++; 11 } 12 13 for(int i = 1; i<=N; i++){ 14 if(count[i] == N - 1){ 15 return i; 16 } 17 } 18 19 return -1; 20 } 21 }
LeetCode 997. Find the Town Judge
标签：count blog span note hashset input ida represent and
原文地址：https://www.cnblogs.com/Dylan-Java-NYC/p/12047222.html
