977. Squares of a Sorted Array

Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order.

Follow up: Squaring each element and sorting the new array is very trivial, could you find an O(n) solution using a different approach?

• Time : O(n)
• Space : O(1) (except result)

class Solution {
public:
    vector<int> sortedSquares(vector<int>& nums) {
        vector<int> res;
        int l = 0, r = nums.size() - 1;
        while(l <= r) {
            if(abs(nums[l]) < abs(nums[r])) {
                res.push_back(nums[l] * nums[l++]);
            } else {
                res.push_back(nums[r] * nums[r--]);
            }
        }
        return res;
    }
};