四种语言刷算法之合并两个有序链表

力扣21. 合并两个有序链表

1、C

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2){
    if(list1==NULL)return list2;
    if(list2==NULL)return list1;
    struct ListNode* head = (struct ListNode*)malloc(sizeof(struct ListNode));
    head->next = NULL;
    head->val = -1;
    struct ListNode*p = head;
    while(list1!=NULL&&list2!=NULL){
        if(list1->val<=list2->val){
            p->next = list1;
            list1 = list1->next;
        }
        else{
            p->next = list2;
            list2 = list2->next;
        }
        p = p->next;
        p->next = NULL;
    }
    if(list1!=NULL){
        p->next = list1;
    }
    else{
        p->next = list2;
    }
    return head->next;
}

2、C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        if(list1==nullptr)return list2;
        if(list2==nullptr)return list1;
        ListNode *head = new ListNode(-1);
        ListNode* p = head;
        while(list1!=nullptr&&list2!=nullptr){
            if(list1->val<=list2->val){
                p->next = list1;
                list1 = list1->next;
            }
            else{
                p->next = list2;
                list2 = list2->next;
            }
            p = p->next;
            p->next = nullptr;
        }
        if(list1!=nullptr){
            p->next = list1;
        }
        if(list2!=nullptr){
            p->next = list2;
        }
        return head->next;
    }
};

3、JAVA

/**
 * 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) {
        if(list1==null)return list2;
        if(list2==null)return list1;
        ListNode head = new ListNode(-1);
        ListNode p = head;
        while(list1!=null&&list2!=null){
            if(list1.val<=list2.val){
                p.next = list1;
                list1 = list1.next;
            }
            else{
                p.next = list2;
                list2 = list2.next;
            }
            p = p.next;
            p.next = null;
        }
        if(list1!=null){
            p.next = list1;
        }
        if(list2!=null){
            p.next = list2;
        }
        return head.next;
    }
}

4、Python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def mergeTwoLists(self, list1, list2):
        """
        :type list1: Optional[ListNode]
        :type list2: Optional[ListNode]
        :rtype: Optional[ListNode]
        """
        if list1 is None:return list2
        if list2 is None:return list1
        head = ListNode()
        p = head
        while list1 is not None and list2 is not None:
            if list1.val<=list2.val:
                p.next = list1
                list1 = list1.next
            else:
                p.next = list2
                list2 = list2.next
            p = p.next
            p.next = None
            if list1 is not None:
                p.next = list1
            if list2 is not None:
                p.next = list2
        return head.next