977. Squares of a Sorted Array

1. Description

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

2. Example

Example 1:
Input: nums = [-4,-1,0,3,10]
Output: [0,1,9,16,100]
Explanation: After squaring, the array becomes [16,1,0,9,100].
After sorting, it becomes [0,1,9,16,100].

Example 2:
Input: nums = [-7,-3,2,3,11]
Output: [4,9,9,49,121]

3. Constraints

• 1 <= nums.length <= $10^4$
• $-10^4$ <= nums[i] <= $10^4$
• nums is sorted in non-decreasing order.

4. Follow up

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

5. Solutions

Two Pointers(Follow up)

n = nums.size()
Time complexity: O(n)
Space complexity: O(1)

class Solution {
public:
    vector<int> sortedSquares(vector<int> &nums) {
        vector<int> result(nums.size());
        for (int i = result.size() - 1, left = 0, right = nums.size() - 1; left <= right; --i) {
            if (abs(nums[left]) > abs(nums[right])) {
                result[i] = nums[left] * nums[left];
                ++left;
            } else {
                result[i] = nums[right] * nums[right];
                --right;
            }
        }

        return result;
    }
};