我正在学习考试，我在调试链表练习考试时遇到问题。我对他希望我们做的删除功能的不同修改有问题。具体来说，我的deleteEven是一个无穷无尽的外观，我的deleteNthNode不能正常工作。因为我正在努力解决这两个问题，我甚至不知道从哪里开始删除列表中的所有其他元素。在我转移到堆栈和队列之前，我想要完全理解这个主题，我很感激帮助！ ：）
以下是我的代码：
/*
Q1:
Try implementing the functions shown in class on your own:
check: node creation
check: insertion at the end of a linked list,
check: insertion at the head of a linked list,
check: a list printing function.
Q2:
check: Write a recursive printList() function.
Q3:
check: Write a recursive tailInsert() function.
Q4:
check: Write a function that inserts nodes at the beginning of the linked list.
Q5:
check: Write a recursive function that prints a linked list in reverse order.
The function signature is: void printReverse(node *head);
Q6:
check: Write an iterative destroyList() function that frees all the nodes in a linked list.
Q7:
check: Now implement destroyList() recursively.
Q8:
- Write a function that deletes the nth element from a linked list.
If the linked list doesn't even have n nodes, don't delete any of them.
The function signature is: node *deleteNth(node *head, int n).
- Try implementing the function iteratively and recursively.
- (In terms of how to interpret n, you can start counting your nodes from zero or one; your choice.)
Q9:
- Write a function that deletes every other element in a linked list.
- (Try writing it both ways: one where it starts deleting at the head of the list,
- and one where it starts deleting at the element just after the head of the list.)
- Can you write this both iteratively and recursively?
Q10:
- Write a function that deletes all even integers from a linked list.
Q11:
- Write a function that takes a sorted linked list and an element to be inserted into that linked list,
and inserts the element in sorted order.
The function signature is: node *insertSorted(node *head, int n);
Q12:
- One of the problems with the first insertNode() function from today is that it
requires us to call it using head = insertNode(head, i).
That's a bit dangerous, because we could forget the "head =" part very easily.
Re-write the function so that it takes a pointer to head,
thereby allowing it to directly modify the contents of head without any need for a return value.
The function signature is: void insertNode(node **head, int data).
The function will be called using insertNode(&head, i).
*/
//come back to
#include <stdio.h>
#include <stdlib.h>
// Basic linked list node struct; contains 'data' and 'next' pointer.
// What happens if we type "node *next" instead of "struct node *next"?
typedef struct node
{
// data field
int data;
// the next node in the list
struct node *next;
} node;
// Allocate a new node. Initialize its fields. Return the pointer.
// We call this from our insertion functions.
node *createNode(int data)
{
node *ptr = NULL;
ptr = malloc(sizeof(node));
if(ptr == NULL)
{
printf("space could not be allocated\n");
return NULL;
}
ptr->data = data;
ptr->next = NULL;
return ptr;
}
// Insert into the end of the linked list. Return the head of the linked list.
// (What is the order (Big-Oh) of this function?)
/*
node *insertNode(node *head, int data)
{
node *temp;
if (head == NULL)
return createNode(data);
for(temp = head; temp->next != NULL; temp = temp->next)
;
temp->next = createNode(data);
return head;
}
*/
node *insertNodeFront(node *head, int data)
{
node *temp;
if(head == NULL)
return createNode(data);
temp = createNode(data);
temp->next = head;
return temp;
}
// Simple function to print the contents of a linked list.
void printList(node *head)
{
if (head == NULL)
{
printf("Empty List\n");
return;
}
for(; head != NULL; head = head->next)
printf("%d ", head->data);
printf("\n");
}
void printListRecursiveHelper(node *head)
{
if (head == NULL)
return;
printf("%d%c", head->data, (head->next == NULL) ? '\n' : ' ');
printListRecursiveHelper(head->next);
}
void printListRecursive(node *head)
{
if (head == NULL)
{
printf("empty list\n");
return;
}
printListRecursiveHelper(head);
}
// Q3: - Write a recursive tailInsert() function.
node *tailInsert(node *head, int data)
{
if(head->next == NULL)
{
node *temp;
temp = createNode(data);
temp->next = NULL;
head->next = temp;
return temp;
}
return tailInsert(head->next, data);
}
//Q5: Write a recursive function that prints a linked list in reverse order.
void printReverse(node *head)
{
if (head == NULL)
return;
printReverse(head->next);
printf("%d ", head->data);
}
// Q6: - Write an iterative destroyList() function that frees all the nodes in a linked list.
// Got code from internet, memorize it
/* Function to delete the entire linked list */
void destroyList (struct node** head)
{
struct node* current = *head;
struct node* next;
while (current != NULL)
{
next = current->next;
free(current);
current = next;
}
*head = NULL;
}
// Q7: - Now implement destroyList() recursively.
// Look up online, need to examine why it deson't work
node *destroyListRecursive(node * head)
{
if (head != NULL)
{
destroyListRecursive(head->next);
free(head);
}
return NULL;
}
/* Q8:
- Write a function that deletes the nth element from a linked list.
- If the linked list doesn't even have n nodes, don't delete any of them.
- Try implementing the function iteratively and recursively.
- (In terms of how to interpret n, you can start counting your nodes from zero or one; your choice.)
*/
node *deleteNth(node *head, int n)
{
/*
int i;
node*current;
node *prev;
current = head;
while(i = 0; i < n; i++)
{
current = current->next;
}
prev = current;
current = head->next->next;
*/
return head;
}
/*
Q9:
- Write a function that deletes every other element in a linked list.
- (Try writing it both ways: one where it starts deleting at the head of the list,
- and one where it starts deleting at the element just after the head of the list.)
- Can you write this both iteratively and recursively?
*/
/* deletes alternate nodes of a list starting with head */
//got code from http://www.geeksforgeeks.org/delete-alternate-nodes-of-a-linked-list/
void deleteAltHead(struct node *head)
{
if (head == NULL)
return;
struct node *node = head->next;
if (node == NULL)
return;
/* Change the next link of head */
head->next = node->next;
/* free memory allocated for node */
free(node);
/* Recursively call for the new next of head */
deleteAltHead(head->next);
}
void deleteOtherTail()
{
}
//Q10: - Write a function that deletes all even integers from a linked list.
void deleteEvenInts(node **head)
{
}
// Q11: - Write a function that takes a sorted linked list and an element to be inserted into that linked list,
// and inserts the element in sorted order.
node *insertSorted(node *head, int n)
{
struct node *current;
struct node *newNode = createNode(n);
/* Special case for the head end */
if (head == NULL || head->data >= newNode->data)
{
newNode->next = head;
head = newNode;
}
else
{
/* Locate the node before the point of insertion */
current = head;
while (current->next != NULL &&
current->next->data < newNode->data)
{
current = current->next;
}
newNode->next = current->next;
current->next = newNode;
}
return current;
//or should it return head?
}
// Q12: Re-write the insertNode() function so that it takes a pointer to head
void insertNode(node **head, int data)
{
node *newNode = createNode(data);
while (*head != NULL)
{
head = &(*head)->next;
}
newNode->next = *head;
*head = newNode;
}
// Q10: Write a function that deletes all even integers from a linked list.
void deleteEven(node **head)
{
node *current = *head;
node *next = current;
node *prev = NULL;
for ( ; current != NULL; )
{
next = current->next;
if( current->data %2)
{
if(prev != NULL)
{
prev->next = next;
free(current);
current = next;
}
else
{
free(current);
current = next;
}
}
else
{
prev = current;
current = next;
}
}
}
//Q8: Write a function that deletes the nth element from a linked list. If the linked list doesn't even have n nodes, don't delete any of them.
node *deleteNthNode(node *head, int n)
{
int i = 0;
int nBigger = 0;
node *current = head;
node *prev = current;
for ( i = 0; i < n; i++)
{
prev = current;
current = current->next;
if (current == NULL)
{
nBigger = 1;
}
}
if(nBigger == 1)
{
return head;
}
prev = current->next;
free(current);
return head;
}
int main(void)
{
int i, r;
// The head of our linked list. If we don't initialize it to NULL, our
// insertNode() function might segfault.
node *head = NULL;
srand(time(NULL));
// Populate the linked list with random integers. We are inserting into the
// head of the list each time.
for (i = 0; i < 10; i++)
{
printf("Inserting %d...\n", r = rand() % 20 + 1);
insertNode(&head, r);
}
head = insertNodeFront(head, 1);
tailInsert(head, 5);
// Print the linked list.
printList(head);
printf("\n");
printReverse(head);
printf("\n\n");
// Print the linked list using our recursive function.
printListRecursive(head);
//destroyList(&head);
deleteAltHead(head);
printf("\n");
printList(head);
{
if (head == NULL)
return;
struct node *node = head->next;
if (node == NULL)
return;
/* Change the next link of head */
head->next = node->next;
/* free memory allocated for node */
free(node);
/* Recursively call for the new next of head */
}
deleteEven(&head);
// head = destroyListRecursive(head);
printf("\n");
printList(head);
node *head2 = NULL;
insertNode(&head2, 1);
insertNode(&head2, 2);
insertNode(&head2, 4);
printf("\n");
printList(head2);
insertSorted(head2, 3);
printf("\n");
deleteNthNode(head, 1);
printList(head2);
//destroyListRecursive(head2);
system("PAUSE");
return 0;
}