LeetCode不定时刷题——Merge Two Sorted Lists

21. Merge Two Sorted Lists

递归

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1==null){
            return l2;
        }else 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;
        }
    }
}

非递归

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        ListNode tmp = new ListNode(0);
        ListNode res = tmp;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                tmp.next = l1;
                l1 = l1.next;
            } else {
                tmp.next = l2;
                l2 = l2.next;

            }
            tmp = tmp.next;
        }
        if (l1 != null) {
            tmp.next = l1;

        }

        if (l2 != null) {
            tmp.next = l2;

        }

        return res.next;
    }
}

来源：CSDN

作者：loserChen.

链接：https://blog.csdn.net/qq_35564813/article/details/104076694