fn main() {
    let empty = vec![];
    let all_eq = vec![2,2,2,2];
    let not_eq = vec![1,6,5,1,6];

    assert!(is_all_same(&empty));
    assert!(is_all_same2(&empty));
    assert!(is_all_same3(&empty));
    assert!(is_all_same(&all_eq));
    assert!(is_all_same2(&all_eq));
    assert!(is_all_same3(&all_eq));
    assert_eq!(is_all_same(&not_eq), false);
    assert_eq!(is_all_same2(&not_eq), false);
    assert_eq!(is_all_same3(&not_eq), false);
}


fn is_all_same(arr: &[usize]) -> bool {
    if arr.is_empty() {
        return true;
    }
    let first = arr[0];
    arr.iter().all(|&item| item == first)
}

fn is_all_same2(arr: &[usize]) -> bool {
    arr.iter().min() == arr.iter().max()
}

fn is_all_same3<T: PartialEq>(arr: &[T]) -> bool {
    arr.windows(2).all(|w| w[0] == w[1])
}