Swap Nodes in Pairs
25 Dec 2015###Task1 Given a linked list, swap every two adjacent nodes and return its head.
Have you met this question in a real interview? Yes Example Given 1->2->3->4, you should return the list as 2->1->4->3.
Challenge Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
###java ####Iterative
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
/**
* @param head a ListNode
* @return a ListNode
*/
public ListNode swapPairs(ListNode head) {
// Write your code here
if (head == null || head.next == null) {
return head;
}
ListNode dummy = new ListNode(0);
dummy.next = head;
head = dummy;
while (head.next != null && head.next.next != null) {
ListNode n1 = head.next;
ListNode n2 = head.next.next;
head.next = n2;
n1.next = n2.next;
n2.next = n1;
head = n1;
}
return dummy.next;
}
}
Recursive
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
/**
* @param head a ListNode
* @return a ListNode
*/
public ListNode swapPairs(ListNode head) {
// Write your code here
if (head == null || head.next == null) {
return head;
}
ListNode n1 = head;
ListNode n2 = head.next;
n1.next = swapPairs(n2.next);
n2.next = n1;
return n2;
}
}
###Points
- head = n1; move head to n1 instead of n2 !!!!