use std::collections::HashSet;

fn remove_duplicate_words(s: &str) -> String {
    let v: Vec<&str> = s.split(" ").collect();
    let mut set = HashSet::new();
    let mut arr = Vec::new();
    let mut res = String::new();

    for i in 0..v.len() {
        if !set.contains(&v[i]) {
            set.insert(&v[i]);
            arr.push(&v[i]);
        }
    }
    for i in 0..arr.len() {
        if i == arr.len() - 1 {
            res.push_str(arr[i]);
        } else {
            res.push_str(&String::from(format!("{} ", arr[i])));
        }
    }

    res
}

// Rust test example:
extern crate rand;
#[allow(unused_imports)]
use self::rand::Rng;

fn solution(s: &str) -> String {
    let v: Vec<&str> = s.split(" ").collect();
    let mut set = HashSet::new();
    let mut arr = Vec::new();
    let mut res = String::new();

    for i in 0..v.len() {
        if !set.contains(&v[i]) {
            set.insert(&v[i]);
            arr.push(&v[i]);
        }
    }
    for i in 0..arr.len() {
        if i == arr.len() - 1 {
            res.push_str(arr[i]);
        } else {
            res.push_str(&String::from(format!("{} ", arr[i])));
        }
    }

    res
}

#[test]
fn sample_test_cases() {
  assert_eq!(remove_duplicate_words("alpha beta beta gamma gamma gamma delta alpha beta beta gamma gamma gamma delta"), "alpha beta gamma delta");
  assert_eq!(remove_duplicate_words("my cat is my cat fat"), "my cat is fat");
}

#[test]
fn random_test_cases() {
    let mut str = ["Bitcoin", "Bitcoin", "LiteCoin", "LiteCoin", "Ripple", "Dash", "Ripple", "Dash", "Lisk", "DarkCoin", "Monero", "Ethereum", "Classic", "Mine", "ProofOfWork", "ProofOfStake", "cat", "cat", "cat", "Steem", "Dogecoin", "Waves", "Factom", "MadeSafeCoin", "BTC", "BTC", "BTC", "BTC"];
    for _ in 0..100 {
        rand::thread_rng().shuffle(&mut str);
        let start = rand::thread_rng().gen_range(0, str.len() - 5);
        let s = &str[start..start + 5];
        let mut r = String::new();
        for i in 0..s.len() {
            if i == s.len() - 1 {
                r.push_str(s[i]);
            } else {
                r.push_str(&String::from(format!("{} ", s[i])));
            }
        }
        assert_eq!(remove_duplicate_words(&r), solution(&r));
    }
}