count ordered elements in vector

count.rs

fn main() {
    let v1 = vec![1, 1, 1, 1, 2, 2, 1, 1, 5, 5, 5]
        .into_iter()
        .enumerate()
        .fold(vec![], |mut coll, (idx, val)| {
            if idx == 0 {
                [coll, [(val, 1)].to_vec()].concat()
            } else {
                let last_idx = coll.len() - 1;
                let (prev_val, last) = coll[last_idx];
                    
                if val == prev_val {
                    coll[last_idx] = (val, last + 1);

                    coll
                } else {
                    [coll, [(val, 1)].to_vec()].concat()
                }
            }
        });
        
    dbg!(v1);
}