Leetcode21--->merge two Sorted Lists (merge two sorted single-linked lists)

title: give two sorted single linked list, merge two single linked list, return the result after merging;

Problem solving Ideas:

The solution is still very simple, but the following points need to be noted:

1. Returns NULL if all two linked lists are empty;

2. If the list 1 is empty, the head node of the linked list 2 is returned, whereas if the list 2 is empty, the head node of the linked list 1 is returned;

3. Two linked lists are not empty:

Compare the value of the head node of the two list, which is small, which is the head node of the new linked list;

example:l1:1->3->5; L2:2->4->6->7;: head = l1, at which point head.next = L1.next or L2

The code is as Follows:

1 /**2 * Definition for singly-linked List.3 * public class ListNode {4 * int val;5 * ListNode next;6 * ListNode (int x) {val = x;}7  * }8  */9  public classSolution {Ten      publiclistnode mergetwolists (listnode l1, listnode l2) { one         if(L1 = =NULL&& L2 = =NULL) a             return NULL; -         if(L1 = =NULL) -             returnl2; the         if(L2 = =NULL) -             returnl1; -ListNode head =NULL; -         if(l1.val >L2.val) +         { -Head =l2; +Head.next =mergetwolists (l1, l2.next); a         } at         Else -         { -Head =l1; -Head.next =mergetwolists (l1.next, l2); -         } -         returnhead; in     } -}

Leetcode21--->merge two Sorted Lists (merge two sorted single-linked lists)