13. Roman to Integer
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 beforeV
(5) andX
(10) to make 4 and 9.X
can be placed beforeL
(50) andC
(100) to make 40 and 90.C
can be placed beforeD
(500) andM
(1000) to make 400 and 900.
Given a roman numeral, convert it to an integer.
Example 1:
Input: s = "III" Output: 3
Example 2:
Input: s = "IV" Output: 4
Example 3:
Input: s = "IX" Output: 9
Example 4:
Input: s = "LVIII" Output: 58 Explanation: L = 50, V= 5, III = 3.
Example 5:
Input: s = "MCMXCIV" Output: 1994 Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Constraints:
1 <= s.length <= 15
s
contains only the characters('I', 'V', 'X', 'L', 'C', 'D', 'M')
.- It is guaranteed that
s
is a valid roman numeral in the range[1, 3999]
.
Rust Solution
struct Solution;
use std::collections::HashMap;
impl Solution {
fn roman_to_int(s: String) -> i32 {
let map: HashMap<char, i32> = vec![
('I', 1),
('V', 5),
('X', 10),
('L', 50),
('C', 100),
('D', 500),
('M', 1000),
]
.into_iter()
.collect();
let mut sum = 0;
let mut last = 0;
for c in s.chars() {
if let Some(&v) = map.get(&c) {
if v > last {
sum += v - last - last;
} else {
sum += v
}
last = v;
}
}
sum
}
}
#[test]
fn test() {
assert_eq!(Solution::roman_to_int(String::from("III")), 3);
assert_eq!(Solution::roman_to_int(String::from("IV")), 4);
assert_eq!(Solution::roman_to_int(String::from("IX")), 9);
assert_eq!(Solution::roman_to_int(String::from("LVIII")), 58);
assert_eq!(Solution::roman_to_int(String::from("MCMXCIV")), 1994);
}
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