Leetcode daily question (745. prefix and suffix search)

Design a special dictionary with some words that searchs the words in it by a prefix and a suffix.

Implement the WordFilter class:

WordFilter(string[] words) Initializes the object with the words in the dictionary.
f(string prefix, string suffix) Returns the index of the word in the dictionary, which has the prefix prefix and the suffix suffix. If there is more than one valid index, return the largest of them. If there is no such word in the dictionary, return -1.

Example 1:

Input
[“WordFilter”, “f”] > [[[“apple”]], [“a”, “e”]]
Output
[null, 0]

Explanation
WordFilter wordFilter = new WordFilter([“apple”]);
wordFilter.f(“a”, “e”); // return 0, because the word at index 0 has prefix = “a” and suffix = 'e".

Constraints:

• 1 <= words.length <= 15000
• 1 <= words[i].length <= 10
• 1 <= prefix.length, suffix.length <= 10
• words[i], prefix and suffix consist of lower-case English letters only.
• At most 15000 calls will be made to the function f.

---

Treat each word alphabetically into suffix#prefix Combination form , Then you can query , The time complexity of query is O(1), What we should pay attention to here is , Every suffix#prefix Of key Only need to correspond to one of the largest index Just fine , Because that's what the query requires

---

use std::collections::HashMap;

struct WordFilter {
    
    m: HashMap<String, i32>,
}

/** * `&self` means the method takes an immutable reference. * If you need a mutable reference, change it to `&mut self` instead. */
impl WordFilter {
    
    fn new(words: Vec<String>) -> Self {
    
        let mut m = HashMap::new();
        for (i, word) in words.into_iter().enumerate() {
    
            let mut prefix = String::new();
            for pc in word.chars() {
    
                prefix.push(pc);
                let mut suffix = String::new();
                for sc in word.chars().rev() {
    
                    suffix.insert(0, sc);
                    *m.entry(suffix.clone() + "#" + &prefix).or_insert(0) = i as i32;
                }
            }
        }
        Self {
     m }
    }

    fn f(&self, prefix: String, suffix: String) -> i32 {
    
        *self.m.get(&(suffix + "#" + &prefix)).unwrap_or(&-1)
    }
}