use std::collections::HashSet;

struct Solution {}

impl Solution {
    pub fn contains_duplicate(nums: Vec<i32>) -> bool {
        let mut set = HashSet::new();
        for num in nums {
            if !set.insert(num) {
                return true;
            }
        }
        false
    }
}

fn main() {
    println!("{}", Solution::contains_duplicate(vec![1,2,3,4,1]));
}