Leetcode
2020.05.02 18:25

997. Find the Town Judge

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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. 1 <= N <= 1000
  2. trust.length <= 10000
  3. trust[i] are all different
  4. trust[i][0] != trust[i][1]
  5. 1 <= trust[i][0], trust[i][1] <= N


aclass Solution {
    public int findJudge(int N, int[][] trust) {
        Map<Integer, Integer> hmap = new HashMap<>();
        
        if(trust.length == 0){
            return 1;
        }
        
        for(int i=0; i<trust.length; i++){
            Integer people = trust[i][0];
            Integer tpeople = trust[i][1];
            
            hmap.put(people, hmap.getOrDefault(people,0)-1);
            hmap.put(tpeople, hmap.getOrDefault(tpeople,0)+1);
        }
        
        for(Map.Entry<Integer, Integer> item : hmap.entrySet()){
            Integer tpeople = item.getKey();
            Integer tcount = item.getValue();
            
            if(tcount == N - 1){
                return tpeople;
            }
        }
        
        return -1;
    }
}


class Solution {
    public int findJudge(int N, int[][] trust) {
        int[] trusted = new int[N];
        
        for(int i=0; i<trust.length; i++){
            int people = trust[i][0];
            int tpeople = trust[i][1];
            trusted[tpeople-1]++;
            trusted[people-1]--;
        }
        
        for(int i=0; i<trusted.length; i++){
            if(trusted[i] == N - 1){
                return i+1;
            }
        }
        
        return -1;
    }
}

[문제] https://leetcode.com/problems/find-the-town-judge/


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