从单链通函列表中删除特定节点

Question

I have been figuring out how to eliminate all 'A' nodes from the text file, "AHHHHHAAAAHHAAHAHHAHAHAAHAAHHA" I have been able to write the delete node function, but it focuses on removing head only, but I want this function to be able to read the file and remove all 'A' and print out only all H's. Here is my delete node function

struct Node
{
    char data;
    Node* pPrev;
    Node* pNext;
};    

void deleteNode(Node * android)
{
   Node * pTemp = android->pNext;
   android->data = pTemp->data;
   android->pNext = pTemp->pNext;
   free(pTemp);
}

Here is the another delete node function I found here that I tried to modify, I think it will not work.

void deleteNode2(Node * android)
{
   Node * pNext;
   Node * pHead;
   Node * pTail;
   Node * pTemp = android->pNext;

   if(android->pNext == 'A')
   {
       pTemp = pNext;

       if(pHead = pTail)
       {
           pHead = pTail = NULL;
       }
       else
       {
           pHead = pHead->pNext;
       }
   } 
   free(pTemp);
}

in the int main()

while( fscanf(pInFile, "%c", &c) != EOF)
    {
        appendNode( pTail, c);

        // display the list
        displayList( pTail->pNext);

    };

    cout << endl;
    cout << "'A' got removed from the List." << endl << endl;

    deleteNode2(pTail->pNext);
    displayList(pTail->pNext);

Answer 1

The line if(android->pNext == 'A') will give you a compilation error: pNext is a Node* , and you want to compare data. Replace that with if (android->pNext.data == 'A') .

Another issue is that you are making an assignment in an if conditional expression, rather than a comparison: if(pHead = pTail) will not compare the pointers, but instead assign pHead to pTail and evaluate to true (as in, enter the if statement) if pTail was not null. Just fix that by using the == operator.

And yet, there are more issues in your code. deleteNode will not work if there's only one element left. And there's nothing in the program traversing the list in order to find all nodes that you want to remove.

Assuming you'd put this snippet in your main function, you should try something like this:

Node* deleteNode(Node* android)
{
   if (android->next == android) { // only one element
       free(android);
       return NULL;
   } else {
       Node * pTemp = android->pNext;
       android->data = pTemp->data;
       android->pNext = pTemp->pNext;
       free(pTemp);
       return android;
   }
}

size_t listSize(const Node* pNode) {
    if (!pNode) return 0;
    const Node* pStart = pNode;
    size_t n = 0;
    do {
        pNode = pNode->pNext;
        n++;
    } while (pNode != pStart);
    return n;
}

Node * pTemp = pTail;
size_t len = listSize(pTail);
for (unsigned int i = 0 ; i < len ; i++) {
   if (pTemp.data == 'A') {
       pTemp = deleteNode(pTemp);
   } else {
       pTemp = pTemp->next;
   }
}

This is a tougher challenge than it seems, because we're dealing with a circular list. It's a matter of knowing when to stop the loop. In this case, I just counted the number of nodes before the program starts removing them. The first traversal is safe, because it does not modify the list. I've already done significant changes to this, but if anyone notices something wrong, I will be pleased to know.

Just to finish the answer: the circular linked list might be a requirement, but you can make things much easier if you simply prevent the program from appending 'A' characters. Again, it depends on what your final goal is and what you are being demanded.