题目链接

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题目描述

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。

解题思路

递归

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;
    }
}

迭代

public class Solution {
   
    public ListNode Merge(ListNode list1,ListNode list2) {
   
        if (list1==null) return list2;
        if (list2==null) return list1;
        ListNode cur = new ListNode(0), head = cur;
        while (list1!=null && list2!=null) {
   
            if (list1.val > list2.val) {
   
                cur.next = list2;
                list2 = list2.next;
            } else {
   
                cur.next = list1;
                list1 = list1.next;
            }
            cur = cur.next;
        }
        if (list1 == null) cur.next = list2;
        else cur.next = list1;
        return head.next;
    }
}