Leetcode: merge two ordered linked lists_ twenty-one

Ideas

Basic shift double pointer , And the idea of merging

subject

Merge two ascending linked lists into a new Ascending Link list and return . The new linked list is made up of all the nodes of the given two linked lists . 

Example 1：

 Input ：l1 = [1,2,4], l2 = [1,3,4]
 Output ：[1,1,2,3,4,4]

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Example 2：

 Input ：l1 = [], l2 = []
 Output ：[]

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Example 3：

 Input ：l1 = [], l2 = [0]
 Output ：[0]

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Tips ：

• The range of the number of nodes in the two linked lists is [0, 50]
• -100 <= Node.val <= 100
• l1 and l2 All according to Non decreasing order array

Related Topics

• recursive
• Linked list
• 1887
• 0

Code

        public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
            //  Virtual head nodes are very useful 
            ListNode dummy = new ListNode();
            //  Pointer of the result linked list 
            ListNode p = dummy;
            //  Double pointer 
            ListNode p1 = l1;
            ListNode p2 = l2;
            while (p1 != null && p2 != null) {
                if (p1.val < p2.val) {
                    p.next = p1;
                    //  Double pointer movement 
                    p1 = p1.next;
                } else {
                    p.next = p2;
                    p2 = p2.next;
                }
                //  Don't forget to move the result pointer 
                p = p.next;
            }
            //  Connect the long section directly to the result list 
            if (p1 != null) {
                p.next = p1;
            } else {
                p.next = p2;
            }
            return dummy.next;
        }

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