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