chochim chochim - 20 days ago 5
Python Question

Implementing binary search tree

I am extremely sorry for being so naive. I am trying to implement a binary search tree in python (part of learning python in a way). I tried to google it, but I am unable to point out where I have faltered. What I am interested in knowing is not an implementation, but why my code is not working. Any help is really appreciated.

The code goes like as follows -

class Node:
rChild,lChild,data = None,None,None

def __init__(self,key):
self.rChild = None
self.lChild = None
self.data = key

class Tree:
root,size = None,0
def __init__(self):
self.root = None
self.size = 0

def insert(self,node,someNumber):
if node is None:
node = Node(someNumber)
else:
if node.data > someNumber:
self.insert(node.rchild,someNumber)
else:
self.insert(node.rchild, someNumber)
return

def main():
t = Tree()
t.root = Node(4)
t.root.rchild = Node(5)
print t.root.data #this works
print t.root.rchild.data #this works too
t = Tree()
t.insert(t.root,4)
t.insert(t.root,5)
print t.root.data #this fails
print t.root.rchild.data #this fails too

if __name__ == '__main__':
main()

Answer

Here is a quick example of a binary insert:

class Node:
    def __init__(self, val):
        self.l_child = None
        self.r_child = None
        self.data = val

def binary_insert(root, node):
    if root is None:
        root = node
    else:
        if root.data > node.data:
            if root.l_child is None:
                root.l_child = node
            else:
                binary_insert(root.l_child, node)
        else:
            if root.r_child is None:
                root.r_child = node
            else:
                binary_insert(root.r_child, node)

def in_order_print(root):
    if not root:
        return
    in_order_print(root.l_child)
    print root.data
    in_order_print(root.r_child)

def pre_order_print(root):
    if not root:
        return        
    print root.data
    pre_order_print(root.l_child)
    pre_order_print(root.r_child)    

r = Node(3)
binary_insert(r, Node(7))
binary_insert(r, Node(1))
binary_insert(r, Node(5))

     3
    / \
   1   7
      /
     5

print "in order:"
in_order_print(r)

print "pre order"
pre_order_print(r)

in order:
1
3
5
7
pre order
3
1
7
5