Find all numbers disappeared in an array

findAllNumsDisappearedInAnArray.js

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var findDisappearedNumbers = function(nums) {
    let ans = [];
    for(let i=0; i<nums.length; i++) {
        if(nums[Math.abs(nums[i]) - 1] < 0) continue;
        nums[Math.abs(nums[i]) - 1] = -nums[Math.abs(nums[i]) - 1];
    }
    
    for(let i=0; i<nums.length; i++) {
        if(nums[i] > 0) ans.push(i+1);
    }
    
    return ans;
};

// Iterate through the array and negate the element at index equal to the current element - 1
// ex: [4, 2, 1 ,3 , 5, 5] element at 0 = 4 ==> mark element at nums[4 - 1] as -nums[4 - 1]
// at the end, iterate through the array again and add the (index + 1) of elements which are greater than 0 to the ans array  

// Time: O(n)
// Space: O(1)