Invert Binary Tree

[code]/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void invert(TreeNode *root) {
        if(root == NULL)
            return;

        TreeNode *leftNode, *rightNode;
        leftNode = root->left;
        rightNode = root->right;
        root->left = rightNode;
        root->right = leftNode;
        invert(root->left);
        invert(root->right);
    }
    TreeNode* invertTree(TreeNode* root) {
        invert(root);
        return root;

    }
};