24. Swap Nodes in Pairs

最新推荐文章于 2020-03-18 21:48:52 发布

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最新推荐文章于 2020-03-18 21:48:52 发布

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分类专栏： LeetCode LeetCode 文章标签： LeetCode 24 SwapNodes inPairs 邻近节点互换

本文链接：https://blog.youkuaiyun.com/teffi/article/details/54293539

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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。此方法不修改链表值，仅改变节点指向。

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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) {
        if (head == NULL || head->next == NULL) return head;
        ListNode dummy(-1);
        dummy.next = head;

        for (ListNode *prev = &dummy, *cur = prev->next, *next = cur->next;
            next;
            prev = cur, cur = cur->next, next = cur ? cur->next : NULL) {
            prev->next = next;
            cur->next = next->next;
            next->next = cur;
        }

        return dummy.next;
    }
};