题解 | #合并有序链表#

此文仅用于本人学习记录

注意判断是 l 负责的，ptr 只是跑腿的。还有就是这题没说构造函数，我以为 new TreeNode()就行的。

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param l1 ListNode类 
     * @param l2 ListNode类 
     * @return ListNode类
     */
    public ListNode mergeTwoLists (ListNode l1, ListNode l2) {
        // write code here
        ListNode resultIter = new ListNode(0);//这里有点坑
        ListNode resultHead = resultIter;
        ListNode ptr1 = l1;
        ListNode ptr2 = l2;
        while(l1 != null && l2 != null){
            if(l1.val < l2.val){
                l1 = l1.next;
                ptr1.next = null;
                resultIter.next = ptr1;
                resultIter = resultIter.next;
                ptr1 = l1;
            }
            else {
                l2 = l2.next;
                ptr2.next = null;
                resultIter.next = ptr2;
                resultIter = resultIter.next;
                ptr2 = l2;
            }
        }
        if(l1 != null){
            resultIter.next = l1;
        }
        if(l2 != null){
            resultIter.next = l2;
        }
        return resultHead.next;
    }
}