leetcode: Swap Nodes in Pairs

原创于 2013-05-24 10:51:00 发布 · 486 阅读

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本文介绍了一种链表相邻节点交换算法，该算法仅使用常量空间，并且不修改节点值，只改变节点间的连接关系。通过实例演示了如何将链表中每两个相邻节点进行交换。

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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.

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (!head)
            return NULL;
            
        if (head->next == NULL)
            return head;
        
        ListNode *pPre  = NULL;
        ListNode *pCur  = head;
        ListNode *pNext = NULL;
        
        while (pCur && pCur->next)
        {
            if (pPre)
                pPre->next = pCur->next;
            else
                head = pCur->next;
                        
            pPre  = pCur;
            pNext = pCur->next->next;
            pCur->next->next = pCur;
            pCur  = pNext;  
            pPre->next = pCur;
        }     
        return head;      
    }
};