024 Swap Nodes in Pairs

最新推荐文章于 2020-07-06 08:53:44 发布

walter1990

最新推荐文章于 2020-07-06 08:53:44 发布

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分类专栏： Leetcode

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本文详细介绍了如何使用常量空间在链表中交换每两个相邻节点，并提供了实现代码。通过实例演示了如何将链表从单向链表转换为每两个节点一组的双向链表。

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

For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

#include <iostream>
#include <vector>
#include <string>
#include <cstdio>
using namespace std;

struct ListNode
{
	int val;
	ListNode *next;
	ListNode(int x):val(x),next(NULL) {}
};
class Solution {
public:
	ListNode* swapPairs(ListNode* head) {
		if(head == NULL) return head;

		ListNode *h = head;
		ListNode *pre = head;

		for(; head != NULL;) {

			ListNode *cur = head;
			ListNode *next = head->next;

			if(next != NULL) {
				next = next->next;

				if(pre == h) {
					pre = cur->next;
					cur->next->next = cur;
					cur->next = next;
					h = pre;
				} else {
					pre->next = cur->next;
					cur->next->next = cur;
					cur->next = next;
				}
				pre = cur;
				head = pre->next;
			} else {
				break;
			}
		}

		return h;
	}
};