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12. Integer to Roman

Question

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

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

Example1

Input: num = 3
Output: "III"

Example2

Input: num = 4
Output: "IV"

Example3

Input: num = 9
Output: "IX"

Example4

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

Example5

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

Constraints

• 1 <= num <= 3999

解题

题目

首先先简单的翻译一下题目
给你十进位的数字转成罗马数字表示，然後I可以放在V跟X的前面，X可以放在L跟C的前面，而C可以放在D跟M的前面。
像是：IV，V代表的是5，I代表的是1，IV则代表的是4 (5-1)，以此类推。

Think

作法大致上是这样

• 因为IV、IX、XL、XC、CD、CM在计算上有点麻烦，所以我就乾脆把他们一起建在dictionary中。
• 用keys()是为了要抓到dictionary中最大的数，用来除读进来的十进位数，再用商来判断拿来除的罗马数字应该要有几个，余数再拿来除下一轮的dictionary的数。
• 每次算完，就会把罗马数字加上去，一直到最後的余数为0。
• C的程序睡醒再补上。

Code

Python

class Solution:
    def intToRoman(self, num: int) -> str:
        Symbol_dict = {1:'I', 4: 'IV', 5:'V', 9:'IX', 10:'X',
                       40:'XL', 50:'L', 90:'XC', 100:'C',
                       400:'CD', 500:'D', 900:'CM', 1000:'M'}
        
        roman = ""
        index = -1
        keys = list(Symbol_dict.keys())
        
        while num != 0:
            if num // keys[index] == 0:
                if num % keys[index] == 0:
                    roman = Symbol_dict[keys[index]]
                    return roman
                else:
                    num %= keys[index]
                    index -= 1
            else:
                for times in range(num//keys[index]):
                    roman += Symbol_dict[keys[index]]
                    
                num %= keys[index]
                index -= 1

        return roman

C

Result

• Python

  • 

• C

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