Leetcode

# 997. Find the Town Judge

by hooni posted May 02, 2020
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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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