[LeetCode brush question-Python] Square of ordered array

977. Squaring an Ordered Array

977. Squaring an Ordered Array

topic

Given an array of integers nums sorted in non-decreasing order, return a new array consisting of the square of each number, also sorted in non-decreasing order.

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, the array becomes is [0,1,9,16,100]

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

the code

class Solution(object):
    def sortedSquares(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        n=len(nums)
        ans=[-1]*n #新建数组ans = [-1 for _ in range(n)]
        l,r,i=0,n-1,n-1

        while l<=r:
            if nums[l]*nums[l]>nums[r]*nums[r]:
                ans[i]=nums[l]*nums[l]
                l+=1
            else:
                ans[i]=nums[r]*nums[r]
                r-=1
            i-=1
        return ans

       

Summarize

• Review the double pointer, move to the left and right respectively
• ans=[-1]*n #New array ans = [-1 for _ in range(n)]