LeetCode——Invert Binary Tree

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