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Program to change the root of a binary tree using Python
Suppose, we are given a binary tree and a node that is situated at the leaf of the binary tree.We have to make the leaf node the root node of the binary tree. We can do it in the following way −
If a node has a left child, it becomes the right child.
A node's parent becomes its left child. In this process, the parent node's link to that node becomes null, so it will have only one child.
The node structure of the tree is like below −
TreeNode: data: <integer> left: <pointer of TreeNode> right: <pointer of TreeNode> parent: <pointer of TreeNode>
We have to return the root of the converted tree.
So, if the input is like
and the new root is 8; then the inorder representation of the converted tree will be − 2, 3, 4, 5, 7, 6, 8,
The new root node of the tree is 8.
To solve this, we will follow these steps −
Define a function helper() . This will take node, new_par
if node is same as root, then
parent of node := new_par
if left of node is same as new_par, then
left of node := null
if right of node is same as new_par, then
right of node := null
return root
if left of node is not null, then
right of node := left of node
if left of parent of node is same as node, then
left of parent of node := null
left of node := helper(parent of node, node)
parent of node := new_par
return node
return helper(leaf, null)
Let us see the following implementation to get better understanding −
Example
import collections class TreeNode: def __init__(self, data, left = None, right = None, parent = None): self.data = data self.left = left self.right = right self.parent = parent def insert(temp,data): que = [] que.append(temp) while (len(que)): temp = que[0] que.pop(0) if (not temp.left): if data is not None: temp.left = TreeNode(data, parent = temp) else: temp.left = TreeNode(0, parent = temp) break else: que.append(temp.left) if (not temp.right): if data is not None: temp.right = TreeNode(data, parent = temp) else: temp.right = TreeNode(0, parent = temp) break else: que.append(temp.right) def make_tree(elements): Tree = TreeNode(elements[0]) for element in elements[1:]: insert(Tree, element) return Tree def search_node(root, element): if (root == None): return None if (root.data == element): return root res1 = search_node(root.left, element) if res1: return res1 res2 = search_node(root.right, element) return res2 def print_tree(root): if root is not None: print_tree(root.left) print(root.data, end = ', ') print_tree(root.right) def solve(root, leaf): def helper(node, new_par): if node == root: node.parent = new_par if node.left == new_par: node.left = None if node.right == new_par: node.right = None return root if node.left: node.right = node.left if node.parent.left == node: node.parent.left = None node.left = helper(node.parent, node) node.parent = new_par return node return helper(leaf, None) root = make_tree([5, 3, 7, 2, 4, 6, 8]) root = solve(root, search_node(root, 8)) print_tree(root)
Input
root = make_tree([5, 3, 7, 2, 4, 6, 8]) root = solve(root, search_node(root, 8))
Output
2, 3, 4, 5, 7, 6, 8,
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