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.

 

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]

 

Constraints:

• 1 <= nums.length <= 104
• -104 <= nums[i] <= 104
• nums is sorted in non-decreasing order.

class Solution {
    public int[] sortedSquares(int[] nums) {
        int n = nums.length;
        int[] res = new int[n];
        int l = 0, r = n - 1;
        for(int i = n - 1; i > -1; i--) {
            if(Math.abs(nums[l]) > Math.abs(nums[r])) {
                res[i] = nums[l] * nums[l];
                l++;
            }
            else {
                res[i] = nums[r] * nums[r];
                r--;
            }
        }
        return res;
    }
}

two pointers, 有啥规律？从右往左（的平方）由大到小，所以我们设置新数组放进去也是从大到小，一次放一个