leetcode_rust/
roman_to_integer.rs

1#![allow(dead_code)]
2
3// 16ms
4pub fn roman_to_int(s: String) -> i32 {
5    use std::collections::HashMap;
6    let mut map: HashMap<char, i32> = HashMap::new();
7    map.insert('I', 1);
8    map.insert('V', 5);
9    map.insert('X', 10);
10    map.insert('L', 50);
11    map.insert('C', 100);
12    map.insert('D', 500);
13    map.insert('M', 1000);
14
15    let mut sum = 0;
16    let mut i = 0;
17    loop {
18        match s.chars().nth(i) {
19            Some('I') => {
20                match s.chars().nth(i + 1) {
21                    Some('V') => {
22                        sum += 4;
23                        i += 1
24                    }
25                    Some('X') => {
26                        sum += 9;
27                        i += 1
28                    }
29                    _ => sum += 1,
30                };
31            }
32            Some('X') => {
33                match s.chars().nth(i + 1) {
34                    Some('L') => {
35                        sum += 40;
36                        i += 1
37                    }
38                    Some('C') => {
39                        sum += 90;
40                        i += 1
41                    }
42                    _ => sum += 10,
43                };
44            }
45            Some('C') => {
46                match s.chars().nth(i + 1) {
47                    Some('D') => {
48                        sum += 400;
49                        i += 1
50                    }
51                    Some('M') => {
52                        sum += 900;
53                        i += 1
54                    }
55                    _ => sum += 100,
56                };
57            }
58            Some(c) => {
59                sum += *map.get(&c).unwrap();
60            }
61
62            None => {
63                break;
64            }
65        }
66        i += 1;
67    }
68
69    sum
70}
71
72// 20ms
73pub fn roman_to_int2(s: String) -> i32 {
74    use std::collections::HashMap;
75    let mut map: HashMap<u8, i32> = HashMap::new();
76    map.insert(b'I', 1);
77    map.insert(b'V', 5);
78    map.insert(b'X', 10);
79    map.insert(b'L', 50);
80    map.insert(b'C', 100);
81    map.insert(b'D', 500);
82    map.insert(b'M', 1000);
83
84    let mut sum = 0;
85    let s = s.into_bytes();
86    for i in 0..s.len() - 1 {
87        let left = map.get(&s[i]).unwrap();
88        let right = map.get(&s[i + 1]).unwrap();
89        if left < right {
90            sum -= left;
91        } else {
92            sum += left;
93        }
94    }
95    sum += map.get(&s[s.len() - 1]).unwrap();
96
97    sum
98}
99
100#[cfg(test)]
101mod tests {
102    use super::*;
103
104    #[test]
105    fn test1() {
106        assert_eq!(roman_to_int(String::from("LVIII")), 58);
107        assert_eq!(roman_to_int(String::from("MCMXCIV")), 1994);
108    }
109
110    #[test]
111    fn test2() {
112        assert_eq!(roman_to_int2(String::from("LVIII")), 58);
113        assert_eq!(roman_to_int2(String::from("MCMXCIV")), 1994);
114    }
115}
leetcode_rust/roman_to_integer.rs

leetcode_rust/
roman_to_integer.rs
