leetcode Merge k Sorted Lists

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此题利用分治法，将给定的K个链表分成两份，对每一份继续划分，直到最后连个链表进行合并

代码

class Solution {public:    ListNode *mergeKLists(vector<ListNode *> &lists) {                ListNode *newHead = NULL;        int len = lists.size();        if(len==0)            return newHead;                return helper(lists, 0, len-1);    }        ListNode * helper(vector<ListNode*> &lists, int l, int r)    {        if(l<r)        {            int m = (l+r)/2;            return mergeTwoList(helper(lists, l, m), helper(lists, m+1, r));        }                return lists[l];    }        ListNode * mergeTwoList(ListNode *L1, ListNode *L2)    {        ListNode *newHead = new ListNode(0);        ListNode *p = newHead;        ListNode *p1, *p2;        p1 = L1;        p2 = L2;                while(p1!=NULL&&p2!=NULL)        {            if(p1->val>=p2->val)            {                p->next = p2;                p2 = p2->next;                            }            else            {                p->next = p1;                p1 = p1->next;            }                        p = p->next;                    }                if(p1!=NULL)            p->next = p1;                if(p2!=NULL)            p->next = p2;                    return newHead->next;                    }};

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