2017-09-11 LeetCode_024 Swap Nodes in Pairs

24. Swap Nodes in Pairs

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.

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solution:

class Solution {

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public:

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    ListNode* swapPairs(ListNode* head) {

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        if (head == NULL || head->next == NULL) return head;

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        ListNode *p = head;

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        head = head->next;

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        p->next = swapPairs(head->next);

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        head->next = p;

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        return head;

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    }

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};