24. Swap Nodes in Pairs, nodespairs
Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given1->2->3->4
, You shoshould return the list2->1->4->3
.
Your algorithm shocould use only constant space. You may not modify the values in the list, only nodes itself can be changed.
1 /** 2 * Definition for singly-linked list. 3 * struct ListNode { 4 * int val; 5 * ListNode *next; 6 * ListNode(int x) : val(x), next(NULL) {} 7 * }; 8 */ 9 class Solution {10 public:11 ListNode* swapPairs(ListNode* head) {12 13 if(head == NULL || head->next == NULL){14 return head;15 }16 ListNode* newHead = new ListNode(-1);17 ListNode* tail = newHead;18 newHead->next = head;19 20 while(tail && tail->next && tail->next->next){21 ListNode* n = tail->next;22 ListNode* nn = tail->next->next;23 24 //tail->next = nn;25 n->next = nn->next;26 nn->next = n;27 tail->next = nn;28 29 tail = tail->next->next;30 }31 32 return newHead->next;33 }34 };