Given the following data structure:

typedef struct list{
    int num1, num2, num3;
    struct list * next;
} node;

I have this function to delink a node in case it meets a X condition and then link it to another linked list such that I have a linked list with all the delinked nodes.

void delinkNodes(node * register, node ** registerDeleted) {
    node * auxNode;
    while(register->next!= NULL && register->next->next!= NULL) {
        if (helperCheckCondition(register->next)) {
            printf("De-linking node!\n");
            auxNode= register->next->next;
            *registerDeleted= register->next;
            register->next=auxNode;
        }
        else {
            register=register->next;
        }
    }
}

It works since after call the function, if I try to traverse the new linked list it prints out the last delinked node.

The issue is that: It's only the last delinked node. I can't seem to think of a way of linking the delinked nodes together. Then there is the other issue of setting the last node->nextvalue to NULL.

Without writing code in an answer (for now..): What do I need to use in order to solve this in the best possible way? More aux variables...some pattern I might be forgetting...any hints?

CodePudding user response：

Some issues:

• You need to distinguish between the first node to add to the result list and the next ones: only the first time do you need to assign to *registerDeleted, as that is the head node of that list, but the other times you need to extend that list, which does not impact the value of *registerDeleted. So you need a helper variable that will point to the tail of that result list.

• The condition register->next->next != NULL suggests that the tail node could never be candidate for deletion. This is probably not what you intended.

• Don't forget to set the last next pointer in the result list to NULL.

If you cannot figure it out, here is a hidden solution:

void delinkNodes(node * register, node ** registerDeleted) {
if (register == NULL) return;
node * currentNode = register->next;
node * tailNode = NULL;
while (currentNode != NULL) {
if (helperCheckCondition(currentNode)) {
printf("De-linking node!\n");
​register->next = currentNode->next;
if (tailNode == NULL) { // First time only
tailNode = *registerDeleted = currentNode;
​ } else {
​ tailNode = tailNode->next = currentNode;
​ }
tailNode->next = NULL; // Make sure the end of the list is marked!
​ }
​ else {
​register = currentNode;
​ }
currentNode = register->next;
​ }
}