fn dominator(a: &[i64]) -> i64 {
    let mut size = 0i64;
    let mut value = 0;
    let mut index: i64 = 0;

    for (k, &v) in a.iter().enumerate() {
        if size == 0 {
            size += 1;
            value = v;
            index = k as i64;
        } else if value != v {
            size -= 1;
        } else {
            size += 1;
        }
    }

    let candidate = if size > 0 { value } else { -1 };

    let count = a.iter().filter(|&&v| v == candidate).count() as i64;
    if count <= a.len() as i64 / 2 {
        index = -1;
    }

    index
}