1

  2     3

4   5 6   7

     1

  3     2


7    6  5   4

struct TreeNode
{
    int val;
    TreeNode* left;
    TreeNode* right;
};

void reverse_tree(TreeNode& t){

    // end the recursive funtion
    if (t->left == nullptr && t->right == nullptr) return;
   // if (t->right == nullptr) return;

    // do the swap here
    TreeNode tmp = t->left;
    t->left = t->right;
    t->right = tmp;

    // recursively call the function
    reverse_tree(t->left);
    reverse_tree(t->right);

}