随笔-合并两个有序单链表（递归/非递归）

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题目：合并两个有序单链表

递归：

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

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        if(list1.val<=list2.val){
            list1.next=Merge(list1.next,list2);
            return list1;
        }else{
            list2.next=Merge(list1,list2.next);
            return list2;
        }
    }
}

非递归：

链接：https://www.nowcoder.com/questionTerminal/d8b6b4358f774294a89de2a6ac4d9337
来源：牛客网

public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        ListNode newHead = new ListNode(-1);
        ListNode current = newHead;
        while (list1 != null && list2 != null) {
            if (list1.val < list2.val) {
                current.next = list1;
                list1 = list1.next;
            } else {
                current.next = list2;
                list2 = list2.next;
            }
            current = current.next;
        }
        if (list1 != null) current.next = list1;
        if (list2 != null) current.next = list2;
        return newHead.next;
    }
}