FindTheTownJudge.js

/*
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*/


var findJudge = function(N, trust) {
    let in_edges = Array(N).fill(0) 
    let out_edges = Array(N).fill(0)
    if(trust.length === 0) return 1
    for(let pair of trust)
        {
            in_edges[pair[1]-1] += 1
            out_edges[pair[0]-1] += 1
        }
    for (let i = 0; i <= N-1; i++) {
        if (in_edges[i] === N-1 && out_edges[i] === 0) return i+1;
    }
    return -1;
};