LeetCode 24. Swap Nodes in Pairs

原创于 2016-12-30 13:02:57 发布 · 217 阅读

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本文介绍了一种算法，该算法能在常数空间内交换给定链表中的每两个相邻节点，例如将1->2->3->4转换为2->1->4->3。文章详细解释了如何仅通过改变节点指针来实现这一操作，而不修改节点中的实际值。

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) {
        ListNode headNode(0);
        ListNode* preTail = &headNode;
        ListNode* nextHead = head;
        while (true) {
            if ((nextHead == NULL) || (nextHead->next == NULL)) {
                preTail->next = nextHead;
                return headNode.next;
            }
            ListNode* temp = nextHead->next->next;
            preTail->next = nextHead->next;
            nextHead->next->next = nextHead;
            preTail = nextHead;
            nextHead = temp;
        }
    }
};