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Program to find an ancestor which is common of two elements in a binary tree in Python
Suppose we have a binary tree, and we also have two numbers a and b, we have to find the value of the lowest node that has a and b as descendants. We have to keep in mind that a node can be a descendant of itself.
So, if the input is like
a = 6, b = 2, then the output will be 4
To solve this, we will follow these steps −
Define a method solve() this will take root and a, b
if root is null, then
return -1
if value of root is either a or b, then
return value of root
left := solve(left of root, a, b)
right := solve(right of root, a, b)
if left or right is not -1, then
return value of root
return left if left is not same as -1 otherwise right
from the main method call solve(root)
Let us see the following implementation to get better understanding −
Example
class TreeNode: def __init__(self, val, left=None, right=None): self.val = val self.left = left self.right = right class Solution: def solve(self, root, a, b): if not root: return -1 if root.val in (a, b): return root.val left = self.solve(root.left, a, b) right = self.solve(root.right, a, b) if -1 not in (left, right): return root.val return left if left != -1 else right ob = Solution() root = TreeNode(3) root.left = TreeNode(10) root.right = TreeNode(4) root.right.left = TreeNode(8) root.right.right = TreeNode(2) root.right.left.left = TreeNode(6) print(ob.solve(root, 6, 2))
Input
root = TreeNode(3) root.left = TreeNode(10) root.right = TreeNode(4) root.right.left = TreeNode(8) root.right.right = TreeNode(2) root.right.left.left = TreeNode(6) 6, 2
Output
4
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