448-Find-All-Numbers-Disappeared-in-an-Array.js

/**
 * @param {number[]} nums
 * @return {number[]}
 */
const findDisappearedNumbers = (nums) => {
    const result = [];

    for (let i = 0; i < nums.length; i++) {
        let num = Math.abs(nums[i]);
        let idx = num - 1;
        nums[idx] = Math.abs(nums[idx]) * -1;
    }

    for (let i = 0; i < nums.length; i++) {
        if (nums[i] > 0) result.push(i + 1);
    }

    return result;
};