In-place reversal of linked list

reverseList.cpp

// iteration
ListNode* reverseList(ListNode* head) {
    ListNode *pre = nullptr;
    ListNode *cur = head;
    while(cur){
        ListNode *tmp = cur->next;
        cur->next = pre;
        pre = cur;
        cur = tmp;
    }
    return pre;
}

// recursion
ListNode* reverseList(ListNode* head) {
    if(head == nullptr || head->next == nullptr) return head;
    ListNode *node = reverseList(head->next);
    head->next->next = head;
    head->next = nullptr;
    return node;
}