【leetcode每日一题】23.Merge k Sorted Lists-蒲公英云

【leetcode每日一题】23.Merge k Sorted Lists

悠悠 2022-08-04 14:42 254阅读 0赞

题目：Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

解析：可以先归并两个链表，然后依次归并所有链表。代码如下：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1,ListNode* l2)
    {
        if(l1==NULL)
        {
            return l2;
        }
        if(l2==NULL)
        {
            return l1;
        }
        ListNode *result,*curNode;
        if(l1->val<l2->val)
        {
            result=curNode=l1;
            l1=l1->next;
        }
        else
        {
            result=curNode=l2;
            l2=l2->next;
        }
        while(l1!=NULL&&l2!=NULL)
        {
            if(l1->val<l2->val)
            {
                curNode->next=l1;
                l1=l1->next;
            }
            else
            {
                curNode->next=l2;
                l2=l2->next;
            }
            curNode=curNode->next;
        }
        if(l1!=NULL)
        {
            curNode->next=l1;
        }
        if(l2!=NULL)
        {
            curNode->next=l2;
        }
        return result;
    }
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        if(lists.size()==0)
        {
            return NULL;
        }
        ListNode *result=lists[0];
        for(int i=1;i<lists.size();i++)
        {
            result=mergeTwoLists(result,lists[i]);
        }
        return result;
    }
};