LeetCode——合并K个排序链表

题目地址：https://leetcode-cn.com/problems/merge-k-sorted-lists/

解题思路：简单的分治算法

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
private:
     ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode *Head=new ListNode(0);
        ListNode *p,*q,*h;
        p=l1;
        q=l2;
        h=Head;
        while(p&&q){
            if(p->val>=q->val){
                h->next=q;
                h=h->next;
                q=q->next;
            }
            else{
                h->next=p;
                h=h->next;
                p=p->next;
            }
        }
        if(p)
            h->next=p;
        else
            h->next=q;
        return Head->next;
    }
    ListNode *merge(vector<ListNode*>& lists,int l,int r){
        if (l == r)
            return lists[l];
        if (l > r)
            return nullptr;
        int mid = (l + r) >> 1;
        return mergeTwoLists(merge(lists, l, mid), merge(lists, mid + 1, r));
    }
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        return merge(lists,0,lists.size()-1);
    }
};