leetcode226

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode InvertTree(TreeNode root) {
        if (root == null || (root.left == null && root.right == null)) return root;

            TreeNode left = root.left;
            root.left = InvertTree(root.right);
            root.right = InvertTree(left);
            return root;
    }
}

https://leetcode.com/problems/invert-binary-tree/#/description

补充一个使用层次遍历处理的方案，java实现

 class Solution {
     public TreeNode invertTree(TreeNode root) {
         List<TreeNode> nodes = new LinkedList<>();
         if (root != null) {
             nodes.add(root);
         }
         while (!nodes.isEmpty()) {
             int numNodes = nodes.size();
             while (numNodes > 0) {
                 TreeNode node = nodes.remove(0);
                 // push children to the next layer by appending to the end of the list
                 if (node.left != null) {
                     nodes.add(node.left);
                 }
                 if (node.right != null) {
                     nodes.add(node.right);
                 }
                 // flip
                 TreeNode left = node.left;
                 node.left = node.right;
                 node.right = left;
                 numNodes--;
             }
         }
         return root;
     }
 }

补充一个python的实现：

 class Solution:
     def invertTree(self, root: TreeNode) -> TreeNode:
         if root == None:
             return None
         left = root.left
         root.left = self.invertTree(root.right)
         root.right = self.invertTree(left)
         return root