# 951. Flip Equivalent Binary Trees """ for a binarytree 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. given the roots of two binary trees 'root1' and 'root2', return 'true' if the two trees are flip equivalent. """ # Definition for a binary tree node. class TreeNode(object): def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right class Solution(object): def flipEquiv(self, root1, root2): """ :type root1: Optional[TreeNode] :type root2: Optional[TreeNode] :rtype: bool """ s1, s2 = [root1], [root2] while s1 and s2: n1, n2 = s1.pop(), s2.pop() if n1 is None or n2 is None: continue elif not n1 or not n1 or n1.val != n2.val: return False if ( n1.left is None or n2.left is None or n1.left and n2.left and n1.left.val == n2.left.val ): s1.extend([n1.left, n1.right]) else: s1.extend([n1.right, n1.left]) s2.extend([n2.left, n2.right]) return not s1 and not s2 if __name__ == "__main__": obj = Solution() print( obj.flipEquiv( root1=[1, 2, 3, 4, 5, 6, None, None, None, 7, 8], root2=[1, 3, 2, None, 6, 4, 5, None, None, None, None, 8, 7], ) ) print(obj.flipEquiv(root1=[], root2=[])) print(obj.flipEquiv(root1=[], root2=[1]))