226. 翻转二叉树

226. 翻转二叉树

难度简单 774
翻转一棵二叉树。
示例：
输入：
     4
   /  
  2     7
 / \   /
1   3 6   9
输出：
     4
   /  
  7     2
 / \   /
9   6 3   1

    public TreeNode invertTree(TreeNode root) {
        if(root==null){
            return root;
        }
        return hepler(root);
    }
    public TreeNode hepler(TreeNode root) {
        if(root==null){
            return root;
        }
        TreeNode left = root.left;
        TreeNode right= root.right;
        root.left=hepler(right);
        root.right=hepler(left);
        return root;
    }//ok

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root==null){
            return root;
        }
        return hepler(root);
    }
    public TreeNode hepler(TreeNode root) {
        if(root==null){
            return root;
        }
        // TreeNode left = root.left;
        // TreeNode right= root.right;
        // root.left=hepler(right);
        // root.right=hepler(left);
        TreeNode left = hepler(root.left);
        TreeNode right= hepler(root.right);
        root.left = right;
        root.right= left;

        return root;
    }
}