Rust Gym Leetcode 2129 Capitalize the Title Rust Solution

2129. Capitalize the Title

You are given a string title consisting of one or more words separated by a single space, where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that:

If the length of the word is 1 or 2 letters, change all letters to lowercase.
Otherwise, change the first letter to uppercase and the remaining letters to lowercase.

Return the capitalized title.

Example 1:

Input: title = "capiTalIze tHe titLe"
Output: "Capitalize The Title"
Explanation:
Since all the words have a length of at least 3, the first letter of each word is uppercase, and the remaining letters are lowercase.

Example 2:

Input: title = "First leTTeR of EACH Word"
Output: "First Letter of Each Word"
Explanation:
The word "of" has length 2, so it is all lowercase.
The remaining words have a length of at least 3, so the first letter of each remaining word is uppercase, and the remaining letters are lowercase.

Example 3:

Input: title = "i lOve leetcode"
Output: "i Love Leetcode"
Explanation:
The word "i" has length 1, so it is lowercase.
The remaining words have a length of at least 3, so the first letter of each remaining word is uppercase, and the remaining letters are lowercase.

Constraints:

1 <= title.length <= 100
title consists of words separated by a single space without any leading or trailing spaces.
Each word consists of uppercase and lowercase English letters and is non-empty.

2129. Capitalize the Title

struct Solution;

impl Solution {
    fn capitalize_title(title: String) -> String {
        let words: Vec<String> = title
            .split_whitespace()
            .map(Solution::capitalize_word)
            .collect();
        words.join(" ")
    }

    fn capitalize_word(s: &str) -> String {
        let n = s.len();
        let mut res = "".to_string();
        for (i, c) in s.char_indices() {
            if i == 0 {
                if n <= 2 {
                    res.push(c.to_ascii_lowercase());
                } else {
                    res.push(c.to_ascii_uppercase());
                }
            } else {
                res.push(c.to_ascii_lowercase());
            }
        }
        res
    }
}

#[test]
fn test() {
    let title = "capiTalIze tHe titLe".to_string();
    let res = "Capitalize The Title".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
    let title = "First leTTeR of EACH Word".to_string();
    let res = "First Letter of Each Word".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
    let title = "i lOve leetcode".to_string();
    let res = "i Love Leetcode".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
}