使用rust的rayon库函数。

1，rayon库函数优化代码：

fn build_merkle_tree(root: Arc<Mutex<Vec<usize>>>, vect:Vec<usize>, k: Arc<AtomicUsize>, p:usize,q:usize) {
     
    let root_clone = Arc::clone(&root);
    let k_clone = Arc::clone(&k);
    let temp:Vec<_> = vect.par_chunks(2).enumerate().filter_map(|(i,vect_num)| {
        
        let mut root_new = root_clone.lock().expect("出错了");
        let  i = i * 2;
        if i == vect.len()-1 || i == vect.len() -2   {    
            let current_k = k_clone.fetch_add(1, Ordering::SeqCst);                      
            if current_k>=p && current_k<=q  {
                root_new[current_k] = vect_num[0]; 
                }
            }
        if i < vect.len()-1 {
            
            return Some(Hash(vect_num[0],vect_num[1]))
        } else {
            return None;
        }   
    }).collect();

    if !temp.is_empty() {      
        build_merkle_tree( root, temp, k, p,q)
    } else {
            return ;
    }
      
}

2，未使用多线程优化代码。

fn build_merkle_tree_two(root: &mut Vec<usize>, vect:&Vec<usize>, mut k: usize, p:usize,q:usize) -> usize{
    if vect.len() == 0 {
       return k;
    }

    let mut temp = Vec::new();
    for i in (0..vect.len()).step_by(2) {
        if i == vect.len()-1 ||  i == vect.len() -2 {
            root[k] = vect[i];
            k +=1;
        }
        if i < vect.len()-1 {
            temp.push(Hash(vect[i],vect[i+1]));
        }
    }
    k = build_merkle_tree_two( root, &temp, k, 0,0);
    return k;
}