1、题目

12. Integer to Roman

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, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven 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. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: 3

Output: "III"

Example 2:

Input: 4

Output: "IV"

Example 3:

Input: 9

Output: "IX"

Example 4:

Input: 58

Output: "LVIII"

Explanation: L = 50, V = 5, III = 3.

Example 5:

Input: 1994

Output: "MCMXCIV"

Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

2、我的解答（未简化）

 # -*- coding: utf-8 -*-

 # @Time    : 2020/1/30 19:14

 # @Author  : SmartCat0929

 # @Email   : 1027699719@qq.com

 # @Link    : https://github.com/SmartCat0929

 # @Site    :

 # @File    : 12. Integer to Roman(自己想的复杂的算法）.py

 class Solution:

     def intToRoman(self, num: int) -> str:

         numStr = str(num)

         if num < 10:

             if int(numStr[-1]) > 0 and int(numStr[-1]) < 4:

                 units = ""

                 for i in range(0, int(numStr[-1])):

                     units = "I" + units

             elif int(numStr[-1]) == 4:

                 units = "IV"

             elif int(numStr[-1]) == 5:

                 units = "V"

             elif int(numStr[-1]) > 5 and int(numStr[-1]) < 9:

                 units = "V"

                 for i in range(5, int(numStr[-1])):

                     units = units + "I"

             elif int(numStr[-1]) == 9:

                 units = "IX"

             return units

         elif num >= 10 and num <= 99:  # 如果是两位数

             if int(numStr[-1]) == 0:

                 units = ""

             elif int(numStr[-1]) > 0 and int(numStr[-1]) < 4:  # 个位

                 units = ""

                 for i in range(0, int(numStr[-1])):

                     units = "I" + units

             elif int(numStr[-1]) == 4:

                 units = "IV"

             elif int(numStr[-1]) == 5:

                 units = "V"

             elif int(numStr[-1]) > 5 and int(numStr[-1]) < 9:

                 units = "V"

                 for i in range(5, int(numStr[-1])):

                     units = units + "I"

             elif int(numStr[-1]) == 9:

                 units = "IX"

             if int(numStr[-2]) == 1:  # 十位

                 decades = "X"

             elif int(numStr[-2]) > 0 and int(numStr[-2]) < 4:  # 十位

                 decades = ""

                 for j in range(0, int(numStr[-2])):

                     decades = "X" + decades

             elif int(numStr[-2]) == 4:

                 decades = "XL"

             elif int(numStr[-2]) == 5:

                 decades = "L"

             elif int(numStr[-2]) > 5 and int(numStr[-2]) < 9:

                 decades = "L"

                 for j in range(5, int(numStr[-2])):

                     decades = decades + "X"

             elif int(numStr[-2]) == 9:

                 decades = "XC"

             romans = decades + units

             return romans

         elif num >= 100 and num <= 999:  # 如果是三位数

             if int(numStr[-1]) == 0:  # 个位

                 units = ""

             elif int(numStr[-1]) > 0 and int(numStr[-1]) < 4:

                 units = ""

                 for i in range(0, int(numStr[-1])):

                     units = "I" + units

             elif int(numStr[-1]) == 4:

                 units = "IV"

             elif int(numStr[-1]) == 5:

                 units = "V"

             elif int(numStr[-1]) > 5 and int(numStr[-1]) < 9:

                 units = "V"

                 for i in range(5, int(numStr[-1])):

                     units = units + "I"

             elif int(numStr[-1]) == 9:

                 units = "IX"

             if int(numStr[-2]) == 0:  # 十位

                 decades = ""

             elif int(numStr[-2]) > 0 and int(numStr[-2]) < 4:

                 decades = ""

                 for j in range(0, int(numStr[-2])):

                     decades = "X" + decades

             elif int(numStr[-2]) == 4:

                 decades = "XL"

             elif int(numStr[-2]) == 5:

                 decades = "L"

             elif int(numStr[-2]) > 5 and int(numStr[-2]) < 9:

                 decades = "L"

                 for j in range(5, int(numStr[-2])):

                     decades = decades + "X"

             elif int(numStr[-2]) == 9:

                 decades = "XC"

             if int(numStr[-3]) > 0 and int(numStr[-3]) < 4:  # 百位

                 hundreds = ""

                 for j in range(0, int(numStr[-3])):

                     hundreds = "C" + hundreds

             elif int(numStr[-3]) == 4:

                 hundreds = "CD"

             elif int(numStr[-3]) == 5:

                 hundreds = "D"

             elif int(numStr[-3]) > 5 and int(numStr[-3]) < 9:

                 hundreds = "D"

                 for j in range(5, int(numStr[-3])):

                     hundreds = hundreds + "C"

             elif int(numStr[-3]) == 9:

                 hundreds = "CM"

             romans = hundreds + decades + units

             return romans

         elif num >= 1000 and num <= 3999:  # 如果是四位数

             if int(numStr[-1]) == 0:  # 个位

                 units = ""

             elif int(numStr[-1]) > 0 and int(numStr[-1]) < 4:

                 units = ""

                 for i in range(0, int(numStr[-1])):

                     units = "I" + units

             elif int(numStr[-1]) == 4:

                 units = "IV"

             elif int(numStr[-1]) == 5:

                 units = "V"

             elif int(numStr[-1]) > 5 and int(numStr[-1]) < 9:

                 units = "V"

                 for i in range(5, int(numStr[-1])):

                     units = units + "I"

             elif int(numStr[-1]) == 9:

                 units = "IX"

             if int(numStr[-2]) == 0:  # 十位

                 decades = ""

             elif int(numStr[-2]) > 0 and int(numStr[-2]) < 4:

                 decades = ""

                 for j in range(0, int(numStr[-2])):

                     decades = "X" + decades

             elif int(numStr[-2]) == 4:

                 decades = "XL"

             elif int(numStr[-2]) == 5:

                 decades = "L"

             elif int(numStr[-2]) > 5 and int(numStr[-2]) < 9:

                 decades = "L"

                 for j in range(5, int(numStr[-2])):

                     decades = decades + "X"

             elif int(numStr[-2]) == 9:

                 decades = "XC"

             if int(numStr[-3]) == 0:  # 百位

                 hundreds = ""

             elif int(numStr[-3]) > 0 and int(numStr[-3]) < 4:

                 hundreds = ""

                 for j in range(0, int(numStr[-3])):

                     hundreds = "C" + hundreds

             elif int(numStr[-3]) == 4:

                 hundreds = "CD"

             elif int(numStr[-3]) == 5:

                 hundreds = "D"

             elif int(numStr[-3]) > 5 and int(numStr[-3]) < 9:

                 hundreds = "D"

                 for j in range(5, int(numStr[-3])):

                     hundreds = hundreds + "C"

             elif int(numStr[-3]) == 9:

                 hundreds = "CM"

             if int(numStr[-4]) > 0 and int(numStr[-4]) < 4: #千位

                 thousands = ""

                 for j in range(0, int(numStr[-4])):

                     thousands = "M" + thousands

                 romans = thousands + hundreds + decades + units

                 return romans

         elif num > 3999:

             return 0

 print(Solution().intToRoman(400))

3、大神的解法

LeetCode上看到的大神的解法，实在是佩服！ 采用字典将特殊符号记住，随后逐一判断.......

 class Solution:

     def intToRoman(self, num: int) -> str:

         res = ""

         s = 1000

         d = {1: "I", 5: "V", 10: "X", 50: "L", 100: "C", 500: "D", 1000: "M"}

         while num != 0:

             r, temp = divmod(num, s)

             if r == 9:

                 res += d[s] + d[s * 10]

             elif r == 4:

                 res += d[s] + d[s * 5]

             elif r >= 5:

                 res += d[s * 5] + d[s] * (r - 5)

             else:

                 res += d[s] * r

             s = s // 10

             num = temp

         return res

 print(Solution().intToRoman(2964))
												


											
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