Function ring_algorithm::build_subsum_tree

pub fn build_subsum_tree<T>(a: Vec<T>) -> Vec<T> where
    T: Sized + Clone + Zero + for<'x> From<<&'x T as Add>::Output>,
    for<'x> &'x T: Add, 

calc subsum tree

  14
  /\
 5  9
/\  /\
2 3 4 5

use ring_algorithm::build_subsum_tree;
let a = vec![2, 3, 4, 5];
let b = vec![14, 5, 9, 2, 3, 4, 5];
let r = build_subsum_tree::<i32>(a);
assert_eq!(b, r);
let a = vec![2, 3, 4, 5, 6];
let b = vec![20, 14, 6, 5, 9, 6, 0, 2, 3, 4, 5, 6, 0, 0, 0];
let r = build_subsum_tree::<i32>(a);
assert_eq!(b, r);