# 24. Swap Nodes in Pairs
Given a linked list, swap every two adjacent nodes and return its head.
Example:
Given 1->2->3->4, you should return the list as 2->1->4->3.
Note:
- Your algorithm should use only constant extra space.
- You may not modify the values in the list's nodes, only nodes itself may be changed.
# Solution
Approach 1: Swap every two nodes.
# Code (Python)
Approach 1:
# Code (C++)
Approach 1:
/**
* 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) {
ListNode dummyHead(0);
dummyHead.next = head;
ListNode *prev = &dummyHead;
ListNode *curr = head;
while (curr && curr->next)
{
ListNode *nextNext = curr->next->next;
prev->next = curr->next;
curr->next->next = curr;
curr->next = nextNext;
prev = curr;
curr = curr->next;
}
return dummyHead.next;
}
};