Python program to convert a given binary tree to doubly linked list.














































Python program to convert a given binary tree to doubly linked list.



Description:
In a given  Binary Tree (BT), convert it to a Doubly Linked List(DLL). The left and right pointers in nodes are to be used as previous and next pointers respectively in converted DLL. The order of nodes in DLL must be same as Inorder of the given Binary Tree. The first node of Inorder traversal (left most node in BT) must be head node of the DLL.

Program:

class Node(object): #Binary tree Node class has data, left and right child def __init__(self, item): self.data = item self.left = None self.right = None def BTToDLLUtil(root): #This is a utility function to #convert the binary tree to doubly #linked list. Most of the core task #is done by this function. if root is None: return root # Convert left subtree # and link to root if root.left: # Convert the left subtree left = BTToDLLUtil(root.left) # Find inorder predecessor, After # this loop, left will point to the # inorder predecessor of root while left.right: left = left.right # Make root as next of predecessor left.right = root # Make predecessor as # previous of root root.left = left # Convert the right subtree # and link to root if root.right: # Convert the right subtree right = BTToDLLUtil(root.right) # Find inorder successor, After # this loop, right will point to # the inorder successor of root while right.left: right = right.left # Make root as previous # of successor right.left = root # Make successor as # next of root root.right = right return root def BTToDLL(root): if root is None: return root # Convert to doubly linked # list using BLLToDLLUtil root = BTToDLLUtil(root) # We need pointer to left most # node which is head of the # constructed Doubly Linked list while root.left: root = root.left return root def print_list(head): """Function to print the given doubly linked list""" if head is None: return while head: print(head.data, end = " ") head = head.right # Driver Code if __name__ == '__main__': root = Node(10) root.left = Node(12) root.right = Node(15) root.left.left = Node(25) root.left.right = Node(30) root.right.left = Node(36) head = BTToDLL(root) print_list(head)

Output:
25 12 30 10 36 15 
>>> 

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