997. Find the Town Judge

1. Question

In a town, there are n people labeled 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 an array trust where trust[i] = [ai, bi] representing that the person labeled ai trusts the person labeled bi.

Return the label of the town judge if the town judge exists and can be identified, or return -1 otherwise.

2. Examples

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

3. Constraints

  • 1 <= n <= 1000
  • 0 <= trust.length <= 104
  • trust[i].length == 2
  • All the pairs of trust are unique.
  • ai != bi
  • 1 <= ai, bi <= n

4. References

来源:力扣(LeetCode) 链接:https://leetcode-cn.com/problems/find-the-town-judge 著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。

5. Solutions

理解成有向图,则法官的入度为n-1,出度为0.

class Solution {
  public int findJudge(int n, int[][] trust) {
    int[] in = new int[n + 1];
    int[] out = new int[n + 1];

    for(int[] arr : trust) {
      out[arr[0]]++;
      in[arr[1]]++;
    }



    for(int i = 1; i <= n; i++) {
      if(in[i] == n - 1 && out[i] == 0) {
        return i;
      }
    }
    return -1;
  }
}
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