leetcode21

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.

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简单题

没有什么技术含量。

简单循环，codetime上面可能慢一点。

递归的代码量小很多，也很简洁。

/**
 * 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) {
        ListNode headNode = new ListNode(0);
        ListNode result = new ListNode(0);
        headNode.next = result;
        ListNode nextNode = new ListNode(0);
        while(l1 != null || l2 != null)
        {
            nextNode = new ListNode(0);
            if(l1 == null){
                nextNode.val = l2.val;
                l2 = l2.next;
            }else if(l2 == null){
                nextNode.val = l1.val;
                l1 = l1.next;
            }else if(l1.val>l2.val){
                nextNode.val = l2.val;
                l2 = l2.next;
            }else{
                nextNode.val = l1.val;
                l1 = l1.next;
            }

            result.next = nextNode;
            result = result.next;
        }
        return headNode.next.next;
    }
}

public ListNode mergeTwoLists(ListNode l1, ListNode l2){
        if(l1 == null) return l2;
        if(l2 == null) return l1;
        if(l1.val < l2.val){
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        } else{
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
}