use std::collections::HashMap;

pub fn two_sum(nums: Vec<i32>, target: i32) -> Vec<i32> {
    let mut map = HashMap::new();

    for (i, &num) in nums.iter().enumerate() {
        let complement = target - num;
        if let Some(&index) = map.get(&complement) {
            return vec![index as i32, i as i32];
        }
        map.insert(num, i);
    }

    vec![]
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_example_1() {
        let nums = vec![1, 8, 10, 21];
        let target = 18;
        assert_eq!(two_sum(nums, target), vec![1, 2]);
    }

    #[test]
    fn test_example_2() {
        let nums = vec![5, 12, 19, 3];
        let target = 8;
        assert_eq!(two_sum(nums, target), vec![0, 3]);
    }

    #[test]
    fn test_example_3() {
        let nums = vec![6, 6];
        let target = 12;
        assert_eq!(two_sum(nums, target), vec![0, 1]);
    }
}