```
/**
* 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) {
if(root==NULL)return root;
invertTree(root->left); // 1
invertTree(root->right); // 2
swap(root->left,root->right);
return root;
}
};
```

I got this accepted in 0 ms but I don't get how swapping between left child and right child pointers after two recursion works fine in my case.I have seen people doing similar swapping before the two recursive statements(1& 2).So which one is correct.I think I was lucky to get AC.

Please let me know which one is correct solution.And also how can I cross check my own solution for problems like this.Thanks in advance.