LeetCode: Merge k Sorted Lists [022]

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【题目】

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

【题意】

合并K个有序链表

【思路】

归并

【代码】

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* merge(vector<ListNode*>&lists, int start, int end){        if(start==end)return lists[start];        int mid=(start+end)/2;        ListNode*p1=merge(lists, start, mid);        ListNode*p2=merge(lists, mid+1, end);        ListNode*head=NULL, *p=NULL;        while(p1&&p2){            if(p1->val<p2->val){                if(p)p->next=p1;                p=p1;                p1=p1->next;            }            else{                if(p)p->next=p2;                p=p2;                p2=p2->next;            }                        if(head==NULL)head=p;        }        if(p1){            if(p)p->next=p1;            else{p=p1;head=p;}        }        if(p2){            if(p)p->next=p2;            else{p=p2;head=p;}        }        return head;    }    ListNode *mergeKLists(vector<ListNode *> &lists) {int size=lists.size();if(size==0) return NULL;if(size==1) return lists[0];return merge(lists, 0, size-1);    }};

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