LeetCode 226. Invert Binary Tree

/**
 * 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:
    TreeNode* invertTree(TreeNode* root) {
        
        fun(root);
        return root;
    }
    
    void fun(TreeNode* root)
    {
        if(root==NULL)
            return;
        if(root->left!=NULL)
            fun(root->left);
        if(root->right!=NULL)
            fun(root->right);
        
        TreeNode* term = root->left;
        
        root->left = root->right;
        root->right = term;
    }

};