LeetCode Invert Binary Tree

# Definition for a binary tree node.class TreeNode(object):     def __init__(self, x):         self.val = x         self.left = None         self.right = Noneclass Solution(object):    def invertTree(self, root):        """        :type root: TreeNode        :rtype: TreeNode        """        stack = [root]        while stack:            t= stack.pop()            if t:                t.left,t.right = t.right,t.left                stack.append(t.left)                stack.append(t.right)        return rootclass Solution2(object):    def invertTree(self, root):        """        :type root: TreeNode        :rtype: TreeNode        """        if root:            root.left,root.right = root.right,root.left            self.invertTree(root.left)            self.invertTree(root.right)        return rootif __name__ == '__main__':    root  = TreeNode(1)    a = TreeNode(2)    b = TreeNode(3)    root.left=a    root.right=b    Solution().invertTree(root)    print root.left.val,root.right.val