[LeetCode]: Swap Nodes in Pairs方法介绍

Given a linked list, swap every two adjacent nodes and return its head.

You may not modify the values in the list's nodes, only nodes itself may be changed.

Example:

Given 1->2->3->4You should return the list as 2->1->4->3Given 1->2->3You should return the list as 2->1->3难度不大

方法一：二级指针交换
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */

void
swap_ptr(struct ListNode** head) {
	struct ListNode* temp = (*head)->next;
	(*head)->next = (*head)->next->next;
	temp->next = *head;
	*head = temp;
}

struct ListNode* swapPairs(struct ListNode* head) {
	if (!head || !head->next)
		return head;

	if (!head->next->next) {
		swap_ptr(&head);
		return head;
	}

	head->next->next = swapPairs(head->next->next);
	swap_ptr(&head);
	return head;
}

方法二：一级指针交换
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */

void*
swap_ptr(struct ListNode* first, struct ListNode* second) {
	first->next = second->next;
	second->next = first;
	return second;
}

struct ListNode* swapPairs(struct ListNode* head){
    if (!head || !head->next)
		return head;

	if (!head->next->next)
		return (struct ListNode*)swap_ptr(head, head->next);

	head->next->next = swapPairs(head->next->next);
	return (struct ListNode*)swap_ptr(head, head->next);
}