Find the Town Judge | LeetCode 997

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/**
 * @param {number} N
 * @param {number[][]} trust
 * @return {number}
 */
let findJudge = function(N, trust) {
  // store the trust counts in an array. initialize all counts at zero
  // the array has a length of one more than the population for convenience (person 1's count is index 1 of the array. person 2's count is index 2 of the array, etc.)
  // index zero is a dummy value of 0 and will never be changed
  let trustCounts = new Array(N + 1).fill(0);

  // loop over each trust pair in the array
  for (let [i, j] of trust) {
    trustCounts[i] -= 1; // the trusting person needs to be decremented by one
    trustCounts[j] += 1; // the trusted person needs to be incremented by one
  }

  // loop over the trust counts
  for (let i = 1; i < trustCounts.length; i++) {
    // if there is a person with one less trust count than the population, that person is the judge
    if (trustCounts[i] === N - 1) {
      return i;
    }
  }

  // return -1 if there is no judge
  return -1;
};