use std::collections::HashMap;

pub fn find_lucky(arr: Vec<i32>) -> i32 {
    let mut hm = HashMap::<i32, i32>::new();
    for n in arr {
        let entry = hm.entry(n).or_insert(0);
        *entry += 1;
    }
    let mut lucky = Vec::new(); 
    for (k, v) in hm {
        if k == v {
            lucky.push(k);
        }
    }
    let mut max = -1;
    for n in lucky {
        if n > max {
            max = n;
        }
    }
    return max;
}

pub fn main() {
    println!("Expected: 4");
    println!("Got: {}", find_lucky(vec![1, 4, 4, 4, 4, 2, 6]));
}