Rust Program to Get key from HashMap using the value

Get key from HashMap using the value

Rust Programming Language

Problem

Rust program that retrieves a key from a HashMap using its associated value.

Input

use std::collections::HashMap;

fn get_key_by_value<'a, K, V>(map: &'a HashMap<K, V>, value: &V) -> Option<&'a K>

where

    K: std::cmp::Eq + std::hash::Hash,

    V: std::cmp::Eq,

{

    for (key, val) in map {

        if val == value {

            return Some(key);

        }

    }

    None

}

fn main() {

    let mut map = HashMap::new();

    map.insert(1, "one");

    map.insert(2, "two");

    map.insert(3, "three");

    let value = "two";

    let key = get_key_by_value(&map, &value);

    match key {

        Some(k) => println!("Key for value {}: {}", value, k),

        None => println!("No key found for value {}", value),

    }

}{codeBox}

Output

Key for value two: 2{codeBox}

Explanation

This program defines a get_key_by_value function that takes a reference to a HashMap and a reference to a value, and returns an Option containing a reference to the key associated with that value in the map, or None if no such key exists.

The get_key_by_value function iterates over the key-value pairs in the map using a for loop, checking if the value of each pair matches the input value. If a match is found, the corresponding key is returned.

The main function creates a HashMap and inserts three key-value pairs into it. It then calls get_key_by_value to retrieve the key associated with the value "two" and prints the result.