数组——有序数组的平方

题目顺序：代码随想录算法公开课，b站上有相应视频讲解

一、题目

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.

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

题目来源： leetcode

二、题解

排序写法

class Solution {
public:
    vector<int> sortedSquares(vector<int>& nums) {
        int n = nums.size();
        for(int i = 0;i < n;i++){
            nums[i] = nums[i] * nums[i];
        }
        sort(nums.begin(),nums.end());
        return nums;
    }
};

双指针写法

class Solution {
public:
    vector<int> sortedSquares(vector<int>& nums) {
        int n = nums.size();
        vector<int> res(n,0);
        int index = n - 1;
        for(int i = 0,j = n - 1;i <= j;){
            if(nums[i] * nums[i] > nums[j] * nums[j]){
                res[index--] = nums[i] *nums[i];
                i++;
            }
            else{
                res[index--] = nums[j] * nums[j];
                j--;
            }
        }
        return res;
    }
};