Double Pointer Gists: (1) Using double pointer to insert node in a sorted linked list; (2) Using double pointer to remove all elements from a linked list that have value N (3) Using double pointer to remove duplicates from sorted linked list

double_pointer_1.c

void insertNode(LinkedList *newIp, LinkedList *list) {

  LinkedList **lpp;
  LInkedList *lp;

  for (lpp = &list; *lpp != NULL; lpp = &(*lpp)->next) {
    lp = *lpp;
    if (newIp->val < lp->val) {
      newIp->next = lp;
      *lpp = newIp;
      break;
    }
  }
  
  if (*lpp == NULL)
    *lpp = newIp;
}

double_pointer_2.c

void removeNode(int val, LinkedList **list) {
  while (*list) {
    if ((*list)->val == val) {
      *list = (*list)->next;
    }
    else
      list = &(*list)->next;
  }
}

double_pointer_3.cpp

LinkedList *deleteDuplicates(ListNode *head) {
  ListNode **lpp = &head;
  
  int currValue = INT_MAX;
  
  while (*lpp) {
    if ((*lpp)->val == currValue) {
      *lpp = (*lpp)->next;
    }
    else if ((*lpp)->next && (*lpp)->val == (*lpp)->next->val) {
      currValue = (*lpp)->val;
      *lpp = (*lpp)->next;
    }
    else
      lpp = &(*lpp)->next;
  }
  
  return head;
}