leetcode 24. Swap Nodes in Pairs

1.题目

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.

2.思路 

画个图就方便理解了。



class Solution {
public:
ListNode* swapPairs(ListNode* head) {
ListNode* newhead = new ListNode(-1);
newhead->next = head;
ListNode* pre = newhead;
ListNode* cur = head;
while(cur && cur->next){
pre->next = cur->next;
cur->next = cur->next->next;
pre->next->next = cur;
pre = cur;
cur = cur->next;
}
return newhead->next;
}
};