LeetCode: Set Mismatch Solution

1/**
2 * @param {number[]} nums
3 * @return {number[]}
4 */
5var findErrorNums = function (nums) {
6  const N = nums.length
7  const occurrences = Array.from({ length: N }, (_, i) => [i + 1, 0])
8
9  nums.forEach(num => occurrences[num - 1][1]++)
10  return [
11    occurrences.filter(occ => occ[1] === 2)[0][0],
12    occurrences.filter(occ => occ[1] === 0)[0][0],
13  ]
14}