Given a linked list, swap every two adjacent nodes and return its head.
You may not modify the values in the list's nodes. Only nodes itself may be changed.
Example 1:
Input: head = [1,2,3,4] Output: [2,1,4,3]
Example 2:
Input: head = [] Output: []
Example 3:
Input: head = [1] Output: [1]
Constraints:
- The number of nodes in the list is in the range
[0, 100]
. 0 <= Node.val <= 100
Related Topics:
Linked List
Similar Questions:
// OJ: https://leetcode.com/problems/swap-nodes-in-pairs/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
ListNode h, *tail = &h;
while (head && head->next) {
auto p = head, q = head->next;
head = q->next;
q->next = p;
tail->next = q;
tail = p;
}
tail->next = head;
return h.next;
}
};