LeetCode 1153. String Transforms Into Another String

Problem Statement

use std::collections::{HashMap, HashSet};

impl Solution {
    pub fn can_convert(str1: String, str2: String) -> bool {
        if str1.len() != str2.len() {
            return false;
        }
        if str1 == str2 {
            return true;
        }

        let mut map = HashMap::new();
        let mut have = HashSet::new();

        for i in 0..str1.len() {
            let (key, val) = (str1.chars().nth(i).unwrap(), str2.chars().nth(i).unwrap());
            have.insert(val);
            if !map.contains_key(&key) {
                map.insert(key, val);
            } else if *map.get(&key).unwrap() != val {
                return false;
            }
        }

        return map.len() >= have.len() && (have.len() < 26);
    }
}