How to arrange the array into the smallest number in php (code attached)

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Input an array of positive integers, concatenate all the numbers in the array to form a number, and print the smallest number among all the numbers that can be concatenated. For example, if you input the array {3, 32, 321}, the smallest number that these three numbers can be printed out is 321323.
Solution 1
1. Array sorting, using custom sorting rules is a.b>b.a a and b exchange positions
2.Using the usort function

function costomcomp(a,b)
    return a.b > b.a
usort(arr,'costomcomp')
return implode('',arr)

Solution 2: Bubble method
1. Loop the outer layer i
2. Loop j in the inner layer, the judgment condition is j=i 1;j3. Replace arr[i in the inner layer ].arr[j] > arr[j].arr[i] Swap position

<?php
function customComp($a,$b){
        return intval($a.&#39;&#39;.$b) > intval($b.&#39;&#39;.$a);
}
//解法1：自定义排序
function PrintMinNumber($numbers)
{
        usort($numbers,&#39;customComp&#39;);
        return intval(implode(&#39;&#39;,$numbers));
}
$arr=array(3,32,321);
$result=PrintMinNumber($arr);
var_dump($result);

$result=PrintMinNumber2($arr);
var_dump($result);

//解法2：冒泡排序
function PrintMinNumber2($arr)
{
        $length=count($arr);
        for($i=0;$i<$length;$i++){
                for($j=$i+1;$j<$length;$j++){
                        if(intval($arr[$i].&#39;&#39;.$arr[$j])>intval($arr[$j].&#39;&#39;.$arr[$i])){
                                $temp=$arr[$i];
                                $arr[$i]=$arr[$j];
                                $arr[$j]=$temp;
                        }   
                }   
        }   
        return intval(implode(&#39;&#39;,$arr));
}

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