问题描述：把我们常见的阿拉伯数字转化为罗马数字的形式。
拓展：两种形式的相互转换。
思路：将阿拉伯数字拆分为能够被罗马数字整除的形式（比如100、500等），再整合到一起，然后替换字符为我们需要的形式（比如IIII=>IV，VIV=>IX等等）。再使用键值对形式的数组，在实现阿拉伯数字转罗马数字之后，交换键值，就能实现反向转换了。
function solution($number) {
$roman = array(
'M' => 1000,
'D' => 500,
'C' => 100,
'L' => 50,
'X' => 10,
'V' => 5,
'I' => 1
);
//从大到小遍历，拆分阿拉伯数字
foreach($roman as $key=>$item) {
if($number / $item > 0) {
$int = intval($number / $item);
$number -= $int * $item;
for($i=0;$i<$int;$i++) {
$str .= $key;
}
}
}
return str_replace(['IIII','XXXX','CCCC','VIV','LXL','DCD'],['IV','XL','CD','IX','XC','CM'],$str);
}
我们发现，如4、9、40、90这种转换为罗马数字之后还需要做额外的替换，那为何不直接将其添加到数组里面去呢？
function solution(int $number)
{
$roman = [
'M' => 1000,
'CM' => 900,
'D' => 500,
'CD' => 400,
'C' => 100,
'XC' => 90,
'L' => 50,
'XL' => 40,
'X' => 10,
'IX' => 9,
'V' => 5,
'IV' => 4,
'I' => 1
];
foreach($roman as $key=>$item){
//使用str_repeat代替循环
$str.= str_repeat($key,intval($number/$item));
$number %= $value;
}
return $str;
}
//个人感觉这种思想方式也很简单灵巧
function solution($n)
{
$M = ["","M","MM","MMM"];
$C = ["","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"];
$X = ["","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"];
$I = ["","I","II","III","IV","V","VI","VII","VIII","IX"];
return $M[$n/1000].$C[($n % 1000)/100].$X[($n % 100)/10].$I[($n % 10)];
}
另外，如果你有兴趣，或者是有问题想要与我探讨，欢迎来访问我的博客：https:mu-mu.cn/blog
