0448-find-all-numbers-disappeared-in-an-array.js

// problem link https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array
// time complexity O(n)

var findDisappearedNumbers = function(nums) {
    
    const numberSet = new Set();

    for(let i = 1; i < nums.length + 1; i++) {
        numberSet.add(i);
    }

    nums.forEach((element) => {
        if(numberSet.has(element)) {
            numberSet.delete(element);
        }
    });

    return Array.from(numberSet);
};