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How to implement square of ordered array in PHP

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Release： 2023-03-11 10:58:01

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Given an array A of integers sorted in non-decreasing order, return a new array consisting of the square of each number, which is also required to be sorted in non-decreasing order. Today, the editor will introduce the method of realizing the square of ordered array in PHP. You can refer to it if you need it.

How to implement square of ordered array in PHP

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

Example 1:

输入：[-4,-1,0,3,10]
输出：[0,1,9,16,100]

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Example 2:

输入：[-7,-3,2,3,11]
输出：[4,9,9,49,121]

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Solution idea 1

Built-in function solution

Code

class Solution {
    /** 
    * @param Integer[] $A 
    * @return Integer[] 
    */
    function sortedSquares($A) {
        foreach ($A as &$item) {
            $item = $item * $item;
        }
        sort($A);
        return $A;
    }}

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Solution idea 2

Double pointer traversal, and with the help of the new array, after calculating the square The results are placed in the new array from large to small.

class Solution {
    /** 
    * 
    *
    * 2 为自乘 2 次，也是平方 
    * @param Integer[] $A 
    * @return Integer[] 
    */
    function sortedSquares($A) {
        $ans = [];
        $i = 0;
        $j = count($A) - 1;
        $k = count($A) - 1;
        while ($i <= $j) {
            // 原数组是有序的，所以 -$A[$i] > $A[$j] 即为 $A[$i] 的绝对值平方后更大 
            if (-$A[$i] > $A[$j]) {
                $ans[$k--] = $A[$i] ** 2;
                // 左指针向右移动
                
                $i++;
            } else {
                $ans[$k--] = $A[$j] ** 2;
                $j--;
            }
        }
        return $ans;
    }}

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