0977. Squares of a Sorted Array (E)

题目

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.

题意

将递增数组内的数字取平方后再按照大小进行排序。

思路

因为原数组是递增的，所以最大的平方数一定出现在两边。直接用双指针指向两端，用类似归并排序的方法将平方数按照从大到小的顺序插入到结果数组中。

代码实现

Java

class Solution {
    public int[] sortedSquares(int[] nums) {
        int[] ans = new int[nums.length];
        int i = nums.length - 1;
        int left = 0, right = nums.length - 1;
        while (left <= right) {
            int leftSquare = nums[left] * nums[left];
            int rightSquare = nums[right] * nums[right];
            if (leftSquare >= rightSquare) {
                ans[i--] = leftSquare;
                left++;
            } else {
                ans[i--] = rightSquare;
                right--;
            }
        }
        return ans;
    }
}