[LeetCode Hot 100] LeetCode21. 合并两个有序链表

题目描述

思路：新建dummy去"穿针引线"

新建一个dummy节点去"穿针引线"
注意最后返回的是dummy.next

方法一：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        // 创建一个dummy节点
        ListNode dummy = new ListNode();
        ListNode temp = dummy;
        ListNode p = list1, q = list2;
        while (p != null && q != null) {
            if (p.val <= q.val) {
                temp.next = p;
                temp = p;
                p = p.next;
            } else if(p.val > q.val) {
                temp.next = q;
                temp = q;
                q = q.next;
            }
        }
        if (p == null) temp.next = q;
        if (q == null) temp.next = p;
        return dummy.next;
    }
}