997. Find the Town Judge

Problem

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:

• 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 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**.

  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

  Constraints:

• 1 <= n <= 1000

• 0 <= trust.length <= 10^4

• trust[i].length == 2

• All the pairs of trust are unique.

• ai != bi

• 1 <= ai, bi <= n

Solution (Java)

class Solution {
    public int findJudge(int n, int[][] trust) {
        if (trust.length < n - 1) {
            return -1;
        }
        int[] trustScores = new int[n];
        for (int[] t : trust) {
            trustScores[t[1] - 1]++;
            trustScores[t[0] - 1]--;
        }
        for (int i = 0; i < n; i++) {
            if (trustScores[i] == n - 1) {
                return i + 1;
            }
        }
        return -1;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).