fn missing_numbers(arr: &[i32], brr: &[i32]) -> Vec<i32> {
    //Time complexity: O(a+b)
    //Space complexity (ignoring input): O(a+b)
    let mut arr_hash = std::collections::HashMap::new();
    for value in arr {
        match arr_hash.get(value) {
            Some(f) => arr_hash.insert(value, f + 1),
            None => arr_hash.insert(value, 1),
        };
    }
    let mut brr_hash = std::collections::HashMap::new();
    for value in brr {
        match brr_hash.get(value) {
            Some(f) => brr_hash.insert(value, *f + 1),
            None => brr_hash.insert(value, 1),
        };
    }

    let mut missing_values = Vec::new();
    for (&key, frequency_b) in brr_hash.iter(){
        let frequency_a = arr_hash.get(key).unwrap_or(&0);
        if frequency_a <= frequency_b{
            missing_values.push(*key);
        }
    }

    missing_values.sort_unstable();
    missing_values
}