SetMismatch.js

// Source : https://leetcode.com/problems/set-mismatch
// Author : Dean Shi
// Date   : 2017-07-25

/***************************************************************************************
 *
 * The set S originally contains numbers from 1 to n. But unfortunately, due to the
 * data error, one of the numbers in the set got duplicated to another number in the
 * set, which results in repetition of one number and loss of another number.
 *
 * Given an array nums representing the data status of this set after the error. Your
 * task is to firstly find the number occurs twice and then find the number that is
 * missing. Return them in the form of an array.
 *
 * Example 1:
 *
 * Input: nums = [1,2,2,4]
 * Output: [2,3]
 *
 * Note:
 *
 * The given array size will in the range [2, 10000].
 * The given array's numbers won't have any order.
 *
 *
 ***************************************************************************************/

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var findErrorNums = function(nums) {
    const set = new Set()
    let duplicate, sum = (nums.length * (nums.length + 1)) / 2
    for (let n of nums) {
        if (set.has(n)) duplicate = n
        else {
            sum -= n
            set.add(n)
        }
    }
    return [duplicate, sum]
};