Javascript 將阿拉伯數字轉換成羅馬數字

羅馬數字真的很神奇

Examples: They wrote V instead of 5
And wrote IX instead of 9

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首先，瞭解羅馬數字

阿拉伯數字	羅馬數字
1	I
10	X
50	L
100	C
500	D
1000	M

其次，羅馬數字的表示方法中的規則

1、
When a symbol appears after a larger symbol it is added
當一個符號左邊大於右邊時，兩個符號相加表示數值大小
Example: VI = V + I = 5 + 1 = 6

2、
But if the symbol appears before a larger symbol it is subtracted
但是，當符號左邊小於右邊時，右邊符號減去左邊表示數值大小(10以內)
Example: IX = X - I = 10 - 1 = 9

3、
Don’t use the same symbol more than three times in a row (but IIII is sometimes used for 4, particularly on clocks)
不要將一個符號使用超過三次，在鍾的表示裏面例外

解題思路

第一步：將阿拉伯數字拆分開來，可以通過toString()方法(法二)，也可以通過下面的先取餘後除的方法，按照數字從高位到低位的方法逐個將各位的數字獲取出*（法一）*
第二步：構建一個二維數組，將各個位數可能出現的數值大小表示出來
第三步：將大象放進去
第四步：關上門

Javascript代碼（法一）

function convert(num){
            if(isNaN(num)) return num;

            var a=[["","I","II","III","IV","V","VI","VII","VIII","IX"],
                          ["","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"],
                          ["","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"],["","M","MM","MMM"]];
            var roman = "";
            var t=0;
            for(var m = 0, i = 10000; m < 4; m++,i /= 10){
                t=Math.floor((num%i)/(i/10));
                roman += a[3-m][t];
            }
            return roman;
        }

convert(36);

Javascript代碼（法二）

function convert(num){
            if(isNaN(num)) return num;

            var a=[["","I","II","III","IV","V","VI","VII","VIII","IX"],
                          ["","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"],
                          ["","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"],["","M","MM","MMM"]];
            var s = num.toString();
            var arr = [];
            var b = 0;
            for(var m = 0; m < s.length; m++){
              b=a[((s.length)-(m+1))][s[m]];//竟然忘了數組怎麼用，卡了半天，真的難受233
              alert(b);
             arr.push(b);
            }
            b = arr.join("");
            return b;
        }

convert(36);

結語

真的還是要多練習，這麼一個不是很複雜的題目看了將近三個小時，很難受香菇哈哈哈

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