Leetcode - Medium - 12. Integer to Roman - Javascript

Leetcode - Medium - 12. Integer to Roman - Javascript

   晚上9:27       Rain Lin

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12. Integer to Roman

Medium

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9. 
• X can be placed before L (50) and C (100) to make 40 and 90. 
• C can be placed before D (500) and M (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral.

 

Example 1:

Input: num = 3
Output: "III"
Explanation: 3 is represented as 3 ones.

Example 2:

Input: num = 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.

Example 3:

Input: num = 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

 

Constraints:

• 1 <= num <= 3999

 

解題方向：

1. 這邊主要是要搞懂 Roman 規則, 再擬定羅馬與數字對照表

    a. 1 ~ 3 是用 I 表示

    b. 4 ~ 8 是與 V 相關

    c. 9 ~ 10 是和 ‘X’ 相關

程式碼 ：

/**
 * @param {number} num
 * @return {string}
 */
var intToRoman = function(num) {
    if (num < 1 || num > 3999) { return ''; }
    
    const romanList = {
        1000: "M", 
        900: "CM", 
        500: "D", 
        400: "CD", 
        100: "C", 
        90: "XC", 
        50: "L", 
        40: "XL", 
        10: "X", 
        9: "IX", 
        5: "V", 
        4: "IV", 
        1: "I"
    }
    
    const numList = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1];
    let index = 0;
    let result = '';
    let leastNum = num;
    
    while(index < numList.length) {
        const numMod = numList[index];
        index++;
        
        const repeatNum = parseInt(leastNum / numMod);
        
        if (repeatNum === 0) { continue;}
        
        leastNum = leastNum - (repeatNum * numMod);
        result += romanList[numMod].repeat(repeatNum);
        
    }
    
    return result;
};

執行成果：