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

    assert!(is_all_same(all_eq));
    assert_eq!(is_all_same(not_eq), false);
}


fn is_all_same(vec: Vec<usize>) -> bool {
    vec.iter().fold((true, None), {|acc, elem| {
        if let Some(prev) = acc.1 {
            (acc.0 && (prev == elem), Some(elem))
        } else {
            (true, Some(elem))
        }
    }
    }).0
}