951 Flip Equivalent Binary Trees.py

#!/usr/bin/python3
"""
For a binary tree T, we can define a flip operation as follows: choose any node,
and swap the left and right child subtrees.

A binary tree X is flip equivalent to a binary tree Y if and only if we can make
X equal to Y after some number of flip operations.

Write a function that determines whether two binary trees are flip equivalent.
The trees are given by root nodes root1 and root2.



Example 1:

Input: root1 = [1,2,3,4,5,6,null,null,null,7,8], root2 = [1,3,2,null,6,4,5,null,null,null,null,8,7]
Output: true
Explanation: We flipped at nodes with values 1, 3, and 5.
Flipped Trees Diagram


Note:

Each tree will have at most 100 nodes.
Each value in each tree will be a unique integer in the range [0, 99].
"""

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    def flipEquiv(self, root1: TreeNode, root2: TreeNode) -> bool:
        """
        O(N)
        """
        if not root1 and not root2:
            return True
        elif not root1 or not root2:
            return False

        if root1.val != root2.val:
            return False

        return self.flipEquiv(root1.left, root2.left) and self.flipEquiv(root1.right, root2.right) or \
            self.flipEquiv(root1.left, root2.right) and self.flipEquiv(root1.right, root2.left)