leetcode-24-Swap-Nodes-in-Pairs

发表于   |  

描述

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.

分析

吶，补上图：24

解决方案1(C++)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if(head == NULL || head->next == NULL) {
            return head;
        }
        ListNode head_pre(-1);
        head_pre.next = head;
        
        ListNode *pre = &head_pre;
        ListNode *cur = pre->next;
        ListNode *next = cur->next;
        
        for(; next!=NULL; pre=cur, cur=pre->next, next=cur?cur->next: NULL) {
            pre->next = next;
            cur->next = next->next;
            next->next = cur;
        }
        return head_pre.next;
    }
};

相关问题

题目来源