25.合并两个有序的链表 (Easy)*

题目描述*

输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。

示例*

输入：1->2->4, 1->3->4

输出：1->1->2->3->4->4

限制*

0 <= 链表长度 <= 1000

代码*

递归或迭代。

迭代递归

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode *newHead = new ListNode(-1);
        ListNode *cur = newHead;
        while(l1 != nullptr && l2 != nullptr) {
            if(l1->val <= l2->val) {
                cur->next = l1;
                l1 = l1->next;
            }else {
                cur->next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        if(l1 != nullptr) {
            cur->next = l1;
        }else if(l2 != nullptr) {
            cur->next = l2;
        }
        return newHead->next;
    }
};

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if(l1 == nullptr) {
            return l2;
        }
        if(l2 == nullptr) {
            return l1;
        }
        if(l1->val <= l2->val) {
            l1->next = mergeTwoLists(l1->next, l2);
            return l1;
        }else {
            l2->next = mergeTwoLists(l1, l2->next);
            return l2;
        }
    }
};

最后更新: July 23, 2022