lowest-common-ancestor-of-a-binary-tree_236.py

# Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

# According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”


# Example 1:

# 
# Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
# Output: 3
# Explanation: The LCA of nodes 5 and 1 is 3.
# Example 2:

# 
# Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
# Output: 5
# Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
# Example 3:

# Input: root = [1,2], p = 1, q = 2
# Output: 1

# ---------------------------------------Runtime 62 ms Beats 87.12% Memory 28.7 MB Beats 67.1%---------------------------------------


class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    def lowestCommonAncestor(
        self, root: "TreeNode", p: "TreeNode", q: "TreeNode"
    ) -> "TreeNode":
        def iter(node):
            if node:
                if node == p or node == q:
                    return node

                left, right = iter(node.left), iter(node.right)
                return node if left and right else left or right

        return iter(root)