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Hashmaps are one of the most versatile data structures in Rust, providing a way to store key-value pairs. They are part of the standard library and offer a convenient way to associate values with unique keys. In this challenge, you will implement a simple key-value store using Rust's HashMap.

The HashMap type is part of the std::collections module and allows you to perform operations such as inserting, retrieving, and removing elements efficiently.

Your Task

You are tasked with implementing two functions for a key-value store:

  1. insert_or_update: Inserts a new key-value pair into the HashMap, or updates the value if the key already exists.
  2. get_value: Retrieves a value by its key. If the key is not present, return None.

You will write both functions to work with a HashMap<String, String>.

Requirements

insert_or_update

  • Accepts a mutable reference to a HashMap<String, String>, a key of type String, and a value of type String.
  • If the key exists in the map, updates its value.
  • If the key does not exist, inserts the new key-value pair.

get_value

  • Accepts an immutable reference to a HashMap<String, String> and a key of type String.
  • Returns an Option<String>:
    • Some(value) if the key is present.
    • None if the key is absent.

Hints

<details> <summary>Click here to reveal hints</summary>
  • Use the HashMap type from std::collections.
  • To insert or update a value, use the .insert() method of HashMap.
  • To retrieve a value by its key, use the .get() method of HashMap.
</details>
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use std::collections::HashMap;


/// Inserts a key-value pair into the hashmap or updates the value if the key exists.
pub fn insert_or_update(map: &mut HashMap<String, String>, key: String, value: String) {
    // Your code here...
}


/// Retrieves the value associated with a key from the hashmap.
pub fn get_value(map: &HashMap<String, String>, key: String) -> Option<String> {
    // Your code here...
}


// Example usage
pub fn main() {
    let mut store = HashMap::new();


    // Insert a new key-value pair
    insert_or_update(&mut store, "name".to_string(), "Alice".to_string());


    // Update an existing key
    insert_or_update(&mut store, "name".to_string(), "Bob".to_string());


    // Retrieve the value by key
    let value = get_value(&store, "name".to_string());
    assert_eq!(value, Some("Bob".to_string()));


    // Try to get a non-existent key
    let missing = get_value(&store, "age".to_string());
    assert_eq!(missing, None);
}