LeetCode 1138. Alphabet Board Path

Problem Statement

use std::collections::HashMap;

impl Solution {
    pub fn alphabet_board_path(target: String) -> String {
        let mut map: HashMap<char, (i32, i32)> = HashMap::new();
        let alphabet: Vec<char> = "abcdefghijklmnopqrstuvwxyz".chars().collect();
        for i in 0..26 {
            map.insert(alphabet[i], (i as i32 / 5, i as i32 % 5));
        }
        let (mut t, mut ans, mut dx, mut dy) : (String, String, i32, i32) = (
            target.clone(), "".to_string(), 0, 0);
        t.insert(0, 'a');

        for i in 1..t.len() {
            let (cur, prev) = (map.get(&t.chars().nth(i).unwrap()).unwrap(),
            map.get(&t.chars().nth(i - 1).unwrap()).unwrap());
            dx = cur.0 - prev.0; dy = cur.1 - prev.1;
            if dy < 0 {
                ans.push_str(&(0..dy * -1).map(|_| "L").collect::<String>());
            }
            if dx < 0 {
                ans.push_str(&(0..dx * -1).map(|_| "U").collect::<String>());
            }
            if dy > 0 {
                ans.push_str(&(0..dy).map(|_| "R").collect::<String>());
            }
            if dx > 0 {
                ans.push_str(&(0..dx).map(|_| "D").collect::<String>());
            }
            ans.push('!');
        }
        return ans;
    }
}