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. If a trust relationship does not exist in trust array, then such a trust relationship does not exist.

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 <= 104

• trust[i].length == 2

• All the pairs of trust are unique.

• ai != bi

• 1 <= ai, bi <= n

Solution

/**
 * @param {number} n
 * @param {number[][]} trust
 * @return {number}
 */
var findJudge = function(n, trust) {
    var map = Array(n + 1).fill(0).map(() => [0, 0]);
    for (var i = 0; i < trust.length; i++) {
        map[trust[i][0]][0] += 1;
        map[trust[i][1]][1] += 1;
    }
    for (var j = 1; j <= n; j++) {
        if (map[j][0] === 0 && map[j][1] === n - 1) return j;
    }
    return -1;
};

Explain:

nope.

Complexity:

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