Question
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.
Recursive Solution
TODO
Code
class Solution {
public ListNode swapPairs(ListNode head) {
if(head == null || head.next == null) return head;
ListNode n = head.next;
head.next = head.next.next;
n.next = head;
head.next = swapPairs(head.next);
return n;
}
}
Performance
TODO
Iterative Solution
TODO
Code
class Solution {
public ListNode swapPairs(ListNode head) {
if(head == null || head.next == null) return head;
// again, head can change, so use dummy node
ListNode dummyHead = new ListNode(0);
dummyHead.next = head;
ListNode prev = dummyHead;
ListNode n1 = prev.next;
ListNode n2 = prev.next.next;
while(n1 != null && n2 != null) {
n1.next = n2.next;
n2.next = n1;
prev.next = n2;
prev = n1;
n1 = prev != null ? prev.next : null;
n2 = n1 != null ? n1.next : null;
}
return dummyHead.next;
}
}
Performance
TODO