LeetCode 977. Squares of a Sorted Array

原题链接在这里：https://leetcode.com/problems/squares-of-a-sorted-array/

题目：

Given an array of integers A sorted in non-decreasing order, return an array of the squares of each number, also in sorted non-decreasing order.

Example 1:

Input: [-4,-1,0,3,10]
Output: [0,1,9,16,100]

Example 2:

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

Note:

1. 1 <= A.length <= 10000
2. -10000 <= A[i] <= 10000
3. A is sorted in non-decreasing order.

题解：

There could be negative number in A.

Thus have two pointer pointing to head and tail. Compare the squares and move the bigger pointer to the middle.

Time Complexity: O(n). n = A.length.

Space: O(1). regardless res.

AC Java:

class Solution {
    public int[] sortedSquares(int[] A) {
        if(A == null || A.length == 0){
            return A;
        }
        
        int [] res = new int[A.length];
        int i = 0;
        int j = A.length - 1;
        
        for(int po = A.length - 1; po>=0; po--){
            int si = A[i] * A[i];
            int sj = A[j] * A[j];
            if(si > sj){
                res[po] = si;
                i++;
            }else{
                res[po] = sj;
                j--;
            }
        }
        
        return res;
    }
}

类似Merge Sorted Array, Sort Transformed Array.