24 Swap Nodes in Pairs
1. Question
Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given1->2->3->4
, you should return the list as2->1->4->3
.
Your algorithm should use only constant space. You maynotmodify the values in the list, only nodes itself can be changed.
2. Implementation
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode swapPairs(ListNode head) {
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode curNode = dummy;
ListNode first = null, second = null;
while (curNode.next != null && curNode.next.next != null) {
first = curNode.next;
second = curNode.next.next;
first.next = second.next;
second.next = curNode.next;
curNode.next = second;
curNode = first;
}
return dummy.next;
}
}
3. Time & Space Complexity
时间复杂度O(n), 空间复杂度O(1)
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