21. 合并两个有序链表

将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 

示例：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4.

public class MergeTwoSortedLists {    
    private class ListNode {
        int val; 
        ListNode next;
        
        ListNode(int x) {
            val = x;
        }
    }
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null) {
            return l2;
        }
        if(l2 == null) {
            return l1;
        }
        ListNode result = new ListNode(0);
        ListNode curRes = result;
        ListNode curNode1 = l1;
        ListNode curNode2 = l2;
        while(curNode1 != null && curNode2 != null) {
            if(curNode1.val < curNode2.val) {
                curRes.next = new ListNode(curNode1.val);
                curNode1 = curNode1.next;
                curRes = curRes.next;
            }else {
                curRes = new ListNode(curNode2.val);
                curNode2 = curNode2.next;
                curRes = curRes.next;
            }
        }
/*        while(curNode1 != null) {
            curRes.next = new ListNode(curNode1.val);
            curRes = curRes.next;
            curNode1 = curNode1.next;
        }
        
        while(curNode2 != null) {
            curRes.next = new ListNode(curNode2.val);
            curRes = curRes.next;
            curNode2 = curNode2.next;
        }*/
        //无需循环判断，其中一个为空，则将不为空的直接赋值即可
        if(curNode1 != null) {
            curRes.next = curNode1;
        }else {
            curRes.next = curNode2;
        }
        return result.next;
    }
}