[LeetCode]--21. Merge Two Sorted Lists

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.

这里sorted说的是从小到大。

/**
 * 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 ln = new ListNode(0);
        ListNode temp = ln;
        while (l1 != null && l2 != null) {
            if (l1.val<l2.val) {
                temp.next = l1;
                l1 = l1.next;
            }
            else {
                temp.next = l2;
                l2 = l2.next;
            }
            temp = temp.next;
        }
        if (l1 == null && l2 != null) {
            temp.next = l2;
        }
        if (l2 == null && l1 != null) {
            temp.next = l1;
        }
        return ln.next;
    }
}

再看下别人写的代码，其实差不多，这种一般都会采用插入排序。

ListNode dummy = new ListNode(0);
        ListNode lastNode = dummy;

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

        if (l1 != null) {
            lastNode.next = l1;
        } else {
            lastNode.next = l2;
        }

        return dummy.next;