Creating Binary Search Tree in R - r

Question

I have this code for creating a Binary Search Tree in a R6 class.
Creating a Node & BST class. In BST class, I am defining insert_recur function to create the BST by appropriately inserting the data.
library(R6)
Node <- R6Class(
classname = 'Node',
public = list(
val = NULL,
left = NULL,
right = NULL,
initialize = function(val = NULL, left = NULL, right = NULL){
self$val <- val
self$left <- left
self$right <- right
}
)
)
BST <- R6Class(
classname = 'BST',
public = list(
root = NULL,
# node = NULL,
insert = function(data){
if(is.null(self$root)){
self$node <- Node$new(data)
}else{
self$insert_recur(data, self$root)
}
},
insert_recur = function(data, cur_node){
if(data < cur_node$val){
if(is.null(cur_node$self)){
cur_node$left <- Node$new(data)
}else{
insert_recur(data, cur_node$left)
}
}else if(data > cur_node$val){
if(is.null(cur_node$self)){
cur_node$right <- Node$new(data)
}else{
insert_recur(data, cur_node$right)
}
}else{
print('value already in tree')
}
},
get_height = function(cur_node){
if(is.null(cur_node$val)){
return(-1)
}else{
return(max(self$get_height(cur_node$left),self$get_height(cur_node$right))+1)
}
}
)
)
bst <- BST$new()
bst$insert(3)
bst$insert(2)
bst$insert(1)
bst$insert(5)
bst$insert(6)
bst$insert(4)
bst$insert(7)
However I am getting this error -
Error in self$node <- Node$new(data) : cannot add bindings to a locked environment
If I put node <- NULL in the BST class, then the recursion fails & all nodes are NULL.
What will be the correct implementation?

Answer 1

Your Node implementation is fine. The BST isn't quite right though. It should have a NULL root node only. The problem lies in your insert_recur function. It's not possible for cur_node$self to ever be NULL, and the logic would seem to indicate that your if statements should be checking for the absence of cur_node$left and cur_node$right instead. Also, you need to remember to use self$insert_recur. The logic of your get_height argument doesn't seem right to me either. The following implementation seems to work as expected:
BST <- R6Class(
classname = 'BST',
public = list(
root = NULL,
insert = function(data) {
if(is.null(self$root)) {
self$root <- Node$new(data)
} else {
self$insert_recur(data, self$root)
}
},
insert_recur = function(data, cur_node) {
if(data < cur_node$val) {
if(is.null(cur_node$left)) {
cur_node$left <- Node$new(data)
} else {
self$insert_recur(data, cur_node$left)
}
} else if(data > cur_node$val){
if(is.null(cur_node$right)){
cur_node$right <- Node$new(data)
}else{
self$insert_recur(data, cur_node$right)
}
}else{
print('value already in tree')
}
},
get_height = function(cur_node){
if(is.null(cur_node$left) & is.null(cur_node$right)){
return(0)
}else{
return(max(self$get_height(cur_node$left),
self$get_height(cur_node$right)) + 1)
}
}
)
)
This allows
bst <- BST$new()
bst$insert(3)
bst$insert(2)
bst$insert(1)
bst$insert(5)
bst$insert(6)
bst$insert(4)
bst$insert(7)
bst$get_height(bst$root)
#> [1] 3
bst$get_height(bst$root$right)
#> [1] 2
Created on 2022-09-24 with reprex v2.0.2