226. 翻转二叉树

简单

题目描述

解题思路：使用递归交换左右子树

Java

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) return root;
        TreeNode temp = new TreeNode();
        if(root.left != null && root.right != null) {
        	temp = root.left;
        	root.left = root.right;
        	root.right = temp;
        	invertTree(root.left);
        	invertTree(root.right);
        }else if(root.left == null) {
        	root.left = root.right;
        	root.right = null;
        	invertTree(root.left);
        }else if(root.right == null) {
        	root.right = root.left;
        	root.left = null;
        	invertTree(root.right);
        }
        return root;
    }
}

Python

class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if(root == None): return
        if(root.left != None and root.right != None):
            tmp = root.left
            root.left = root.right
            root.right = tmp
            self.invertTree(root.left)
            self.invertTree(root.right)
        elif(root.left != None):
            root.right = root.left
            root.left = None
            self.invertTree(root.right)
        else:
            root.left = root.right
            root.right = None
            self.invertTree(root.left)
        return root