java单链表

public class Solution {

    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        ListNode node = new ListNode(0);
        ListNode head = node;
        while(list1!=null && list2!=null){
            if(list1.val<list2.val){
                node.next = list1;
                list1 = list1.next;
            }else{
                node.next = list2;
                list2 = list2.next;
            }
            node = node.next;
        }
        if(list1!=null){
            node.next = list1;
        }
        if(list2!=null){
            node.next = list2;
        }
        return head.next;
    }

    private void printList(ListNode head){
        while(head!=null){
            System.out.print(head.val+" ");
            head = head.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Solution solution = new Solution();
        int[] array1 = {1, 7, 10, 30};
        int[] array2 = {3, 4, 5, 9, 20, 40};
        ListNode list1 = new ListNode(0);
        ListNode head1 = list1;
        ListNode list2 = new ListNode(0);
        ListNode head2 = list2;
        for(int i=0;i<array1.length;i++){
            list1.next = new ListNode(array1[i]);
            list1 = list1.next;
        }
        for(int i=0;i<array2.length;i++){
            list2.next = new ListNode(array2[i]);
            list2 = list2.next;
        }
        solution.printList(head1.next);
        solution.printList(head2.next);
        solution.printList(solution.Merge(head1.next, head2.next));
    }
}

class ListNode{
    int val;
    ListNode next;
    ListNode(int k){
        val = k;
        next=null;
    }
}