find the difference of two maps in rust

To find the difference of two HashMaps in Rust, we can iterate over the keys of one HashMap and check whether the corresponding keys exist in the other HashMap. If a key is present in one HashMap and not in the other, we can add that key to a new HashMap that will represent the difference.

Here's an example implementation of this approach:

main.rs
use std::collections::HashMap;

fn map_difference<K, V>(map1: &HashMap<K, V>, map2: &HashMap<K, V>) -> HashMap<&K, &V>
where
    K: Eq + std::hash::Hash,
    V: PartialEq,
{
    let mut difference = HashMap::new();

    for (key, value) in map1 {
        if !map2.contains_key(key) || map2.get(key) != Some(value) {
            difference.insert(key, value);
        }
    }

    difference
}
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This function takes in two HashMaps as arguments, and returns a new HashMap containing the keys and values that are present in the first HashMap but not in the second HashMap.

This implementation avoids any ownership or borrowing issues by taking in the two HashMaps as references. Furthermore, by iterating over the HashMap keys instead of the entries or values, we avoid any unnecessary copying or cloning of the values.

Overall, this approach provides an efficient way to find the difference of two HashMaps in Rust.