删除链表的备用节点的 C++ 程序

给定一个单链表，从第二个节点开始删除它的所有备用节点。例如，如果给定的链表是 1->2->3->4->5，那么你的函数应该将它转换为 1->3->5，如果给定的链表是 1->2-> 3->4 然后将其转换为 1->3。

方法1（迭代）：
跟踪要删除的节点的前一个。首先，改变前一个节点的下一个链接，迭代移动到下一个节点。

C++

// C++ program to remove alternate 
// nodes of a linked list 
#include 
using namespace std;
  
// A linked list node 
class Node 
{ 
    public:
    int data; 
    Node *next; 
}; 
  
/* Deletes alternate nodes 
   of a list starting with head */
void deleteAlt(Node *head) 
{ 
    if (head == NULL) 
        return; 
  
    /* Initialize prev and node 
       to be deleted */
    Node *prev = head; 
    Node *node = head->next; 
  
    while (prev != NULL && 
           node != NULL) 
    { 
        /* Change next link of previous 
           node */
        prev->next = node->next; 
  
        // Update prev and node 
        prev = prev->next; 
        if (prev != NULL) 
            node = prev->next; 
    } 
} 
  
/* UTILITY FUNCTIONS TO TEST 
   fun1() and fun2() */
/* Given a reference (pointer to pointer) 
   to the head of a list and an int, push 
   a new node on the front of the list. */
void push(Node** head_ref, 
          int new_data) 
{ 
    /* Allocate node */
    Node* new_node = new Node();
  
    /* Put in the data */
    new_node->data = new_data; 
  
    /* Link the old list off the 
       new node */
    new_node->next = (*head_ref); 
  
    /* Move the head to point to the 
       new node */
    (*head_ref) = new_node; 
} 
  
/* Function to print nodes in a 
   given linked list */
void printList(Node *node) 
{ 
    while (node != NULL) 
    { 
        cout << node->data << " "; 
        node = node->next; 
    } 
} 
  
// Driver code 
int main() 
{ 
    // Start with the empty list 
    Node* head = NULL; 
  
    /* Using push() to construct list 
       1->2->3->4->5 */
    push(&head, 5); 
    push(&head, 4); 
    push(&head, 3); 
    push(&head, 2); 
    push(&head, 1); 
  
    cout << "List before calling deleteAlt() "; 
    printList(head); 
  
    deleteAlt(head); 
  
    cout << "List after calling deleteAlt() "; 
    printList(head); 
  
    return 0; 
} 
// This code is contributed by rathbhupendra

C++

/* Deletes alternate nodes of a list 
   starting with head */
void deleteAlt(Node *head) 
{ 
    if (head == NULL) 
        return; 
  
    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 */
    deleteAlt(head->next); 
} 
// This code is contributed by rathbhupendra

输出：

List before calling deleteAlt() 
1 2 3 4 5 
List after calling deleteAlt() 
1 3 5

时间复杂度： O(n)，其中 n 是给定链表中的节点数。

方法2（递归）：
递归代码使用与方法 1 相同的方法。递归代码简单而简短，但会导致 O(n) 递归函数调用大小为 n 的链表。

C++

/* Deletes alternate nodes of a list 
   starting with head */
void deleteAlt(Node *head) 
{ 
    if (head == NULL) 
        return; 
  
    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 */
    deleteAlt(head->next); 
} 
// This code is contributed by rathbhupendra

时间复杂度： O(n)