数据结构:单向链表系列6--交换相邻两个节点1（交换数据域）

给定一个单向链表,编写函数交换相邻 两个元素

输入: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7

输出: 2 -> 1 -> 4 -> 3 -> 6 -> 5 -> 7

输入: 1 -> 2 -> 3 -> 4 -> 5 -> 6

输出: 2 -> 1 -> 4 -> 3 -> 6 -> 5

通过观察发现:当输入的与元素个数是单数的时候，最后一位不参与交换。 

方法1（迭代)

从头节点开始遍历列表，遍历过程中使用每个节点的下一个节点和当前节点的数据进行交换。

时间复杂度：O(n)

实现过程：

c语言

/* C Program to pairwise swap elements in a given linked list */
#include <stdio.h>
#include <stdlib.h>

/* A linked list node*/
struct Node {
    int data;
    struct Node* next;
};


/* Function to swap two integers at addresses a and b */
void swap(int *a, int *b);

/* Function to pairwise swap elements of a linked list */
void pairWiseSwap(struct Node* head)
{
    struct Node* temp = head;

    /* Traverse further only if there are at-least two nodes left */
    while( temp != NULL && temp->next != NULL)
    {
        /* Swap data of node with its next node's data */
        swap(&temp->data, &temp->next->data);

        /* Move temp by 2 for the next pair*/
        temp = temp->next->next;
    }
}

/* Utility functions */
/* function to swap two integers */
void swap(int *a, int *b)
{
    int temp;
    temp = *a;
    *a = *b;
    *b = temp;
}


/* Funtion to add a node at the beginning of Linked List*/
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*)malloc(sizeof(struct 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(struct Node* node)
{
    while( node != NULL )
    {
        printf("%d ", node->data);
        node = node->next;
    }
    printf("
");
}


/* driver program to test above function */
int main() {

    struct Node* start = NULL;

    /*
        the constructed linked list is:
        1 -> 2 -> 3 -> 4 -> 5
     */
    push(&start ,5);
    push(&start, 4);
    push(&start, 3);
    push(&start, 2);
    push(&start, 1)    ;

    printf("Linked list before calling pairwise swap function
");

    printList(start);

    pairWiseSwap(start);

    printf("Linked list after calling pairwise swap function
");

    printList(start);

    return 0;
}

结果

 java代码：

// Java program to pairwise swap elements of a linked list 
class LinkedList { 
    Node head; // head of list 
  
    /* Linked list Node*/
    class Node { 
        int data; 
        Node next; 
        Node(int d) 
        { 
            data = d; 
            next = null; 
        } 
    } 
  
    void pairWiseSwap() 
    { 
        Node temp = head; 
  
        /* Traverse only till there are atleast 2 nodes left */
        while (temp != null && temp.next != null) { 
  
            /* Swap the data */
            int k = temp.data; 
            temp.data = temp.next.data; 
            temp.next.data = k; 
            temp = temp.next.next; 
        } 
    } 
  
    /* Utility functions */
  
    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    { 
        /* 1 & 2: Allocate the Node & 
                  Put in the data*/
        Node new_node = new Node(new_data); 
  
        /* 3. Make next of new Node as head */
        new_node.next = head; 
  
        /* 4. Move the head to point to new Node */
        head = new_node; 
    } 
  
    /* Function to print linked list */
    void printList() 
    { 
        Node temp = head; 
        while (temp != null) { 
            System.out.print(temp.data + " "); 
            temp = temp.next; 
        } 
        System.out.println(); 
    } 
  
    /* Driver program to test above functions */
    public static void main(String args[]) 
    { 
        LinkedList llist = new LinkedList(); 
  
        /* Created Linked List 1->2->3->4->5 */
        llist.push(5); 
        llist.push(4); 
        llist.push(3); 
        llist.push(2); 
        llist.push(1); 
  
        System.out.println("Linked List before calling pairWiseSwap() "); 
        llist.printList(); 
  
        llist.pairWiseSwap(); 
  
        System.out.println("Linked List after calling pairWiseSwap() "); 
        llist.printList(); 
    } 
} 
/* This code is contributed by Rajat Mishra */

c#代码

// C# program to pairwise swap elements of a linked list 
using System; 
class LinkedList { 
    Node head; // head of list 
  
    /* Linked list Node*/
    public class Node { 
        public int data; 
        public Node next; 
        public Node(int d) 
        { 
            data = d; 
            next = null; 
        } 
    } 
  
    void pairWiseSwap() 
    { 
        Node temp = head; 
  
        /* Traverse only till there are atleast 2 nodes left */
        while (temp != null && temp.next != null) { 
  
            /* Swap the data */
            int k = temp.data; 
            temp.data = temp.next.data; 
            temp.next.data = k; 
            temp = temp.next.next; 
        } 
    } 
  
    /* Utility functions */
  
    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    { 
        /* 1 & 2: Allocate the Node &  
                Put in the data*/
        Node new_node = new Node(new_data); 
  
        /* 3. Make next of new Node as head */
        new_node.next = head; 
  
        /* 4. Move the head to point to new Node */
        head = new_node; 
    } 
  
    /* Function to print linked list */
    void printList() 
    { 
        Node temp = head; 
        while (temp != null) { 
            Console.Write(temp.data + " "); 
            temp = temp.next; 
        } 
        Console.WriteLine(); 
    } 
  
    /* Driver program to test above functions */
    public static void Main(String[] args) 
    { 
        LinkedList llist = new LinkedList(); 
  
        /* Created Linked List 1->2->3->4->5 */
        llist.push(5); 
        llist.push(4); 
        llist.push(3); 
        llist.push(2); 
        llist.push(1); 
  
        Console.WriteLine("Linked List before calling pairWiseSwap() "); 
        llist.printList(); 
  
        llist.pairWiseSwap(); 
  
        Console.WriteLine("Linked List after calling pairWiseSwap() "); 
        llist.printList(); 
    } 
} 
// This code is contributed by Arnab Kundu 

 方法2（递归）

 如果链表中含有两个以上节点,先交换前两个节点,然后递归调用剩下的节点

时间复杂度:O(n)

算法主要部分代码

/* Recursive function to pairwise swap elements 
   of a linked list */
void pairWiseSwap(struct node* head) 
{ 
    /* There must be at-least two nodes in the list */
    if (head != NULL && head->next != NULL) { 
  
        /* Swap the node's data with data of next node */
        swap(&head->data, &head->next->data); 
  
        /* Call pairWiseSwap() for rest of the list */
        pairWiseSwap(head->next->next); 
    } 
} 

以上代码只是交换数据域部分的指针，如果一个节点含有很多字段，将会产生频繁的交换动作。

其他方法：数据结构:单向链表系列7--交换相邻两个节点2

文章来源：https://www.geeksforgeeks.org/pairwise-swap-elements-of-a-given-linked-list/