LeetCode - Swap Nodes in Pairs

Question Definition

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.

Java Solution

public ListNode swapPairs(ListNode head) {
    ListNode cur = head;
    while(head != null && head.next != null){
        int temp = head.val;
        head.val = head.next.val;
        head.next.val = temp;
        head = head.next.next;
    }
    return cur;
}