题目描述
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.
思路
题目很容易理解，把阿拉伯数字转换成罗马数字，难点在于罗马数字中的 4 和 9 需要由另外两个罗马数字 5（10）和 1 组合而成。不过我们也可以发现，罗马数字中比较特殊的组合一共只有 6 种：4,9,40,90,400,900。我们可以把这些特殊的数字组合当成罗马数字中本来就有的基础数字，按照数值从大到小的顺序写进 list 中，之后采用贪心的策略从头遍历这个 list 即可。
代码参考
class Solution:
def intToRoman(self, num: int) -> str:
# Greedy, T: O(1), S: O(1)
digits = [(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")]
roman_digits = []
for value, symbol in digits:
if num == 0:
break
count, num = divmod(num, value)
roman_digits.append(symbol * count)
return ''.join(roman_digits)
