21. Merge Two Sorted Lists

题目：

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.

链接： http://leetcode.com/problems/merge-two-sorted-lists/

一刷，还是需要细心

class Solution(object):
    def mergeTwoLists(self, l1, l2):
        dummy_node = ListNode(0)
        current = dummy_node
        
        while l1 and l2:
            if l1.val <= l2.val:
                current.next = l1
                l1 = l1.next
            else:
                current.next = l2
                l2 = l2.next
            current = current.next
        current.next = l1 if l1 else l2
        return dummy_node.next

2/11/2017, Java

ListNode current必须初始化？

最后需要判断还有剩余的list

/**
 * 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 (l1 == null) return l2;
        else if (l2 == null) return l1;
        
        ListNode head = new ListNode(0);
        ListNode current = head;

        while(l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                current.next = l1;
                l1 = l1.next;
            } else {
                current.next = l2;
                l2 = l2.next;
            }
            current = current.next;
        }
        if (l1 != null) current.next = l1;
        else current.next = l2;

        return head.next;
    }
}