leetcode_rust/problems/p000_0xx/
p000_013.rs

1//! # Description
2//!
3//! Roman numerals are represented by seven different symbols: `I`, `V`, `X`, 
4//! `L`, `C`, `D` and `M`.
5//! 
6//! ```plain
7//! Symbol       Value
8//! I             1
9//! V             5
10//! X             10
11//! L             50
12//! C             100
13//! D             500
14//! M             1000
15//! ```
16//! 
17//! For example, `2` is written as `II` in Roman numeral, just two ones added 
18//! together. `12` is written as `XII`, which is simply `X` + `II`. The number 
19//! `27` is written as `XXVII`, which is `XX` + `V` + `II`.
20//! 
21//! Roman numerals are usually written largest to smallest from left to right. 
22//! However, the numeral for four is not `IIII`. Instead, the number four is 
23//! written as `IV`. Because the one is before the five we subtract it making 
24//! four. The same principle applies to the number nine, which is written as 
25//! `IX`. There are six instances where subtraction is used:
26//! 
27//! - `I` can be placed before `V` (`5`) and `X` (`10`) to make `4` and `9`. 
28//! - `X` can be placed before `L` (`50`) and `C` (`100`) to make `40` and `90`. 
29//! - `C` can be placed before `D` (`500`) and `M` (`1000`) to make `400` and `900`.
30//! 
31//! Given a roman numeral, convert it to an integer.
32//! 
33//!  
34//! 
35//! Example 1:
36//! 
37//! ```plain
38//! Input: s = "III"
39//! Output: 3
40//! Explanation: III = 3.
41//! ```
42//! 
43//! Example 2:
44//! 
45//! ```plain
46//! Input: s = "LVIII"
47//! Output: 58
48//! Explanation: L = 50, V= 5, III = 3.
49//! ```
50//! 
51//! Example 3:
52//! 
53//! ```plain
54//! Input: s = "MCMXCIV"
55//! Output: 1994
56//! Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
57//! ```
58//!  
59//! Constraints:
60//! 
61//! - `1 $\leqslant$ s.length $\leqslant$ 15`
62//! - `s` contains only the characters ('`I`', '`V`', '`X`', '`L`', '`C`', 
63//!     '`D`', '`M`').
64//! - It is guaranteed that `s` is a valid roman numeral in the range `[1, 3999]`.
65//!
66//! Sources: <https://leetcode.com/problems/roman-to-integer/description/>
67
68////////////////////////////////////////////////////////////////////////////////
69
70/// Integer to Roman
71///
72/// # Arguments
73/// * `s` - input string
74pub fn roman_to_int(s: String) -> i32 {
75    let mut val = 0;
76    let mut last_val = 0;
77    let mut temp_digit = 0;
78
79    for ch in s.as_bytes().iter() {
80        let this_val = match *ch {
81            b'I' => 1,
82            b'V' => 5,
83            b'X' => 10,
84            b'L' => 50,
85            b'C' => 100,
86            b'D' => 500,
87            b'M' => 1000,
88            _ => 0,
89        };
90        if last_val == 0 {
91            temp_digit = this_val;
92        } else if this_val == last_val {
93            temp_digit += this_val;
94        } else if this_val < last_val {
95            val += temp_digit;
96            temp_digit = this_val;
97        } else {
98            val += this_val - temp_digit;
99            temp_digit = 0;
100        }
101        last_val = this_val;
102    }
103    val += temp_digit;
104    val
105}