226. Invert Binary Tree

题目大意：
翻转二叉树

思路：递归一下，递归比迭代好写

Python代码：

# 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        """        if root is None:            return None        temp = root.left        root.left = self.invertTree(root.right)        root.right = self.invertTree(temp)        return root# bfs打印树    def printTree(root):    arr = []    arr.append(root)    while len(arr) > 0:        size = len(arr)        for i in range(0, size):            node = arr[0]            print(node.val, ' ',end = '')            if node.left is not None:                arr.append(node.left)            if node.right is not None:                arr.append(node.right)            arr.remove(node)        print()n4 = TreeNode(4)n2 = TreeNode(2)n7 = TreeNode(7)n1 = TreeNode(1)n3 = TreeNode(3)n6 = TreeNode(6)n9 = TreeNode(9)n4.left = n2n4.right = n7# n2.left = n1# n2.right = n3# n7.left = n6# n7.right = n9printTree(n4)root = Solution().invertTree(n4)printTree(root)