Deletion of a node in a BST

class Solution {
    TreeNode *findSuccessor(TreeNode *root){
        if (root->left == nullptr) return root;

        return findSuccessor(root->left);
    }
    public:
    TreeNode *deleteNode(TreeNode *root, int key) {
        if(root == nullptr) return root;

        if(root->val > key) {
            root->left = deleteNode(root->left, key);
        } else if(root->val < key){
            root->right = deleteNode(root->right, key);
        } else {
            if (root->left == nullptr && root->right == nullptr) {
                return nullptr;
            }
            if (root->left == nullptr) return root->right;
            else if (root->right == nullptr) return root->left;

            TreeNode* successor = findSuccessor(root->right);
            root->val = successor->val;
            root->right = deleteNode(root->right, successor->val);
        }
        return root;
    }
};