題目：寫一個函數， 滿足如下條件：

$arr = [
    "Name"  => ‘test‘,
    "Data"  => [
            "Uid"   => 1,
            "Name"  => "eva",
            "Thread" => [
                "ID1"   => 22,
                "ID2"   => 33,
                ],
        ],
    "Title" => "get a string",
]; 

數組樣例如上，

（1）所有key小寫
（2）根據key 升序排列
（3）多維數組 $arr[‘abc‘][‘efg‘] = 1變成 abc.efg = 1
應用場景是什麽？

解答：

<?php
$arr = [
    "Name"  => ‘test‘,
   "Data"  => [
            "Uid"   => 1,
            "Name"  => "eva",
            "Thread" => [
                "ID1"   => 22,
                "ID2"   => 33,
                ]
 
,
        ],
    "Title" => "get a string",
]; 
$testobj = new test();
$testobj->lower($arr);

$prefix = "";
$newArr = [];
$testobj->getPrefix($arr,$prefix,$newArr);
ksort($newArr);
$finalStr = "";
foreach ($newArr as $key=>$value){
    $finalStr .= $key."=".$value."&";
}
 
var_dump(rtrim($finalStr,"&"));
class test{
   
    function getPrefix($arr,&$prefix,&$newArr){
        foreach ($arr as $key=>$value){
            if(is_array($value)){
                $prefix .=$key.".";
                self::getPrefix($value,$prefix,$newArr);
                $prefix = "";
            }else{
                $newArr[$prefix.$key]=$value;
            }
            
        }
        
    }
   
    function lower(&$arr){
        $arr = array_change_key_case($arr);
        foreach ($arr as $key=>&$value){
            if(is_array($value)){
                self::lower($value);
            }
            
        }
    }
}
?>

題目：用戶充值優惠計算方法：

解答：

<?php
    var_dump(discountAmount(800));
    //$amount 為原價
    function discountAmount($amount){
　　　　//價格 => 折扣
        $arr = [
            10 =>1000,　　
            100=> 999,
            200=>998,
            300=>997,
            400=>996,
            500=>995,
            600=>994,
            700=> 993,
            800=> 992,
            900=>991,
            1000=> 990,
            10000=> 989,
            50000=>988,
            500000=> 987,
    ];
    krsort($arr);
    foreach ($arr as $min=>$discount){
        if($amount>=$min){
            return $dicountAmount = $amount * $discount /1000;
        }
    }
    
    }
    
    
?>

遞歸算法學習