_997.java

package com.fishercoder.solutions;

import java.util.HashSet;
import java.util.Set;

/**
 * 997. Find the Town Judge
 *
 * 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
 *
 * 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 <= 1000
 * trust.length <= 10000
 * trust[i] are all different
 * trust[i][0] != trust[i][1]
 * 1 <= trust[i][0], trust[i][1] <= N
 */
public class _997 {
  public static class Solution1 {
    public int findJudge(int N, int[][] trust) {
      int[] trustPoints = new int[N];
      Set<Integer> trustOthers = new HashSet<>();
      for (int[] eachTrust : trust) {
        trustPoints[eachTrust[1] - 1]++;
        trustOthers.add(eachTrust[0]);
      }
      int judge = -1;
      for (int i = 0; i < trustPoints.length; i++) {
        if (trustPoints[i] == N - 1 && !trustOthers.contains(i + 1)) {
            judge = i + 1;
        }
      }
      return judge;
    }
  }
}