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.
** 解题思路**
Using Recursion and Iterative Solution
// Iterative
public ListNode swapPairs(ListNode head) {
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode cur = dummy;
while (cur.next != null && cur.next.next != null) {
ListNode first = cur.next;
ListNode second = cur.next.next;
first.next = second.next;
cur.next = second;
cur.next.next = first;
cur = cur.next.next;
}
return dummy.next;
}
// Recursion
public ListNode swapPairs(ListNode head) {
if (head == null || head.next == null) return head;
ListNode n = head.next;
head.next = swapPairs(head.next.next);
n.next = head;
return n;
}
