leetcode: Swap Nodes in Pairs (C++)

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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.

基本实现思路是设置三个滑动指针 t, p, q 对 ListNode 进行 swap 操作。

<span style="color:#333333;">/** * 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 *t = new ListNode(0); </span><span style="color:#009900;">//设置相邻的 3 个指针 t, p, q</span><span style="color:#333333;">        t->next = head;        ListNode *p = head;        ListNode *q = head->next;        head = q;        while(1) {            t->next = q;            p->next = q->next;            q->next = p;            if(p->next == NULL || p->next->next == NULL) break;            t = p;            p = p->next;            q = p->next;        }        return head;    }};</span>

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