Code shared from the Rust Playground

playground.rs

use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};

#[derive(Debug, Clone)]
struct HashMap<K, V>
where
    K: Eq + Hash + Clone,
    V: Clone,
{
    // Buckets for storing key-value pairs
    buckets: Vec<Option<(K, V)>>,
    // Capacity of the hashmap
    capacity: usize,
}

impl<K, V> HashMap<K, V>
where
    K: Eq + Hash + Clone,
    V: Clone,
{
    fn new(capacity: usize) -> Self {
        HashMap {
            buckets: vec![None; capacity],
            capacity,
        }
    }

    fn hash(&self, key: &K) -> usize {
        let mut hasher = DefaultHasher::new();
        key.hash(&mut hasher);
        hasher.finish() as usize % self.capacity
    }

    fn insert(&mut self, key: K, value: V) {
        let index = self.hash(&key);
        match &mut self.buckets[index] {
            Some((k, _)) if k == &key => {
                // Update existing value
                self.buckets[index] = Some((key, value));
            }
            _ => {
                // Insert new key-value pair
                self.buckets[index] = Some((key, value));
            }
        }
    }

    fn get(&self, key: &K) -> Option<&V> {
        let index = self.hash(key);
        match &self.buckets[index] {
            Some((k, v)) if k == key => Some(v),
            _ => None,
        }
    }

    fn remove(&mut self, key: &K) -> Option<V> {
        let index = self.hash(key);
        match self.buckets[index].take() {
            Some((k, v)) if k == *key => Some(v),
            _ => None,
        }
    }
}

// Example usage
fn main() {
    let mut map = HashMap::new(10);

    map.insert(String::from("key1"), 1);
    map.insert(String::from("key2"), 2);
    map.insert(String::from("key1"), 3); // Update value for "key1"

    println!("{:?}", map);

    println!("Value for key1: {:?}", map.get(&String::from("key1")));
    println!("Value for key2: {:?}", map.get(&String::from("key2")));

    map.remove(&String::from("key1"));
    println!("After removing key1: {:?}", map);
}