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, 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 a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
Example 1:
Input: "III"
Output: 3
Example 2:
Input: "IV"
Output: 4
Example 3:
Input: "IX"
Output: 9
Example 4:
Input: "LVIII"
Output: 58
Explanation: C = 100, L = 50, XXX = 30 and III = 3.
Example 5:
Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
解题思路
这个题目主要是需要便利字符串, 取出对应字符对应值, 需要注意的是, 如果当前的字符比下一个字符小的时候,需要做减法.
时间复杂度: O(n)
示例代码
// 这个方法是简单的封装通过Character获取Int
func getNumFormChar(_ char: Character) -> Int {
switch char {
case "I":
return 1
case "V":
return 5
case "X":
return 10
case "L":
return 50
case "C":
return 100
case "D":
return 500
case "M":
return 1000
default:
return 0
}
}
func romanToInt(_ s: String) -> Int {
var result = 0
let strArray = Array.init(s)
for index in 0..<strArray.count {
let currrentInt = getNumFormChar(strArray[index])
if index < strArray.count - 1 {
let nextInt = getNumFormChar(strArray[index+1])
if currrentInt < nextInt {
result -= currrentInt
}else {
result += currrentInt
}
}else {
result += currrentInt
}
}
return result
}
