两两交换链表中的节点
public ListNode swapPairs(ListNode head) {
if(head == null || head.next == null){
return head;
}
ListNode next = head.next;
head.next = swapPairs(next.next);
next.next = head;
return next;
}
合并两个有序链表
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
else if (l2 == null) {
return l1;
}
else if (l1.val < l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
}
else {
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
}
