LeetCode:Merge k Sorted Lists

Merge k Sorted Lists

Total Accepted: 82424 Total Submissions: 354076 Difficulty: Hard

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

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 Divide and Conquer Linked List Heap

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 (E) Merge Two Sorted Lists (M) Ugly Number II

思路：

归并排序，与数组归并排序类似

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* mergeKLists(vector<ListNode*>& lists) {                if(lists.size() == 0) return NULL;        return mergeSort(lists, 0, lists.size()-1);    }        ListNode *mergeSort(vector<ListNode*>& lists, int s, int e){                if(s==e) return lists[s];        else {            int mid = (s + e)>>1;            ListNode *l1 = mergeSort(lists, s, mid);            ListNode *l2 = mergeSort(lists, mid+1, e);            return merge(l1,l2);        }    }        ListNode *merge(ListNode *l1, ListNode *l2){                if(l1==NULL) return l2;        if(l2==NULL) return l1;        ListNode dummy(0); // 伪头结点        ListNode *p = &dummy;                while(l1 && l2){            if(l1->val < l2->val){                p->next = l1;                l1=l1->next;            }            else {                p->next = l2;                l2=l2->next;            }            p = p->next;        }                p->next = l1!=NULL?l1:l2;        return dummy.next;    }    };