Complete the code below to update P, L, R, and leaves
arrays. 

#### Main loop ####
while(nodes_to_do > 1):
    
####### Find closest pair in matrix d #######
    [minvalue, best_i, best_j] = find_closest_pair(d)
    print(minvalue, best_i, best_j)
    
###### Add new node to tree ########
    #Update P
    #Update L
    #Update R
    #Update leaves

##### We update distance matrix

    nodes_to_do = nodes_to_do - 1
    new_node_ID = new_node_ID + 1

Submit a hardcopy in class on April 9th.