Merge Two Sorted Lists 解答

Question

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Solution

The key to the solution here is to create a new linked list by creating a fake head.

 /**
  * Definition for singly-linked list.
  * public class ListNode {
  *     int val;
  *     ListNode next;
  *     ListNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
         if (l2 == null)
             return l1;
         if (l1 == null)
             return l2;
         ListNode fakeHead = new ListNode(0);
         ListNode tmp = fakeHead;
         ListNode p1 = l1, p2 = l2;
         while (p1 != null && p2 != null) {
             if (p1.val < p2.val) {
                 tmp.next = p1;
                 p1 = p1.next;
             } else {
                 tmp.next = p2;
                 p2 = p2.next;

             }
             tmp = tmp.next;
         }
         while (p1 != null) {
             tmp.next = p1;
             tmp = tmp.next;
             p1 = p1.next;
         }
         while (p2 != null) {
             tmp.next = p2;
             tmp = tmp.next;
             p2 = p2.next;
         }
         return fakeHead.next;
     }
 }