[C + +] leetcode:109 swap Nodes in Pairs (Swap adjacent node locations)

Title:

Given a linked list, swap every, 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. Modify the values in the list, only nodes itself can be changed.

Ideas:

Swap two nodes using the Insert method. Maintains a pre node that represents the previous node that was inserted. Maintains a cur node that represents the node to be inserted. At the same time constructs a virtual head node Dummyhead, maintains the chain list the head node.

Attention:

1. If the linked list is empty, or if there is only one node, the list is returned.

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

2. Maintenance of three nodes.

listnode* dummyhead = new ListNode (0);d ummyhead->next = head; listnode* cur = head; listnode* pre = Dummyhead;

3. Be aware that when the cur itself points to the last node, it is not processed.

while (cur! = NULL && Cur->next! = null)

complexity: O (N)

AC Code:

/** * Definition for singly-linked list. * struct ListNode {*     int val; *     ListNode *next; *     listnode (int x): Val (x), Next (NULL) {} *}; */class Soluti On {public:    listnode *swappairs (ListNode *head) {        listnode* dummyhead = new ListNode (0);        Dummyhead->next = head;        listnode* cur = head;        listnode* pre = Dummyhead;                if (head = = NULL | | head->next = = NULL) return head;        while (cur = null && cur->next! = null)        {            cur = cur->next;            listnode* tmp = cur->next;    Save the last node of the insertion point            Cur->next = pre->next;        Insert the CUR node into            pre->next = cur;                          Pre = cur->next;              Move the pre to the next insertion position            cur->next->next = tmp;        The node after the interchange is connected and the next node of the insertion node            cur = tmp;                    Move cur node        }        return dummyhead->next;    }};

[C + +] leetcode:109 swap Nodes in Pairs (Swap adjacent node locations)