LeetCode题解之 Merge k Sorted Lists

1、题目描述

2、问题分析

使用合并两个链表的方法，逐次合并，效率较低。可以考虑同时合并K个链表。

3、代码

 ListNode* mergeKLists(vector<ListNode*>& lists) {

         ListNode *res = NULL;
         for (vector<ListNode*>::iterator it = lists.begin(); it != lists.end(); it++) {
             res = mergeTwoLists(res, *it);
         }

         return res;
     }

     ListNode *mergeTwoLists(ListNode *list1, ListNode *list2)
     {
         if (list1 == NULL)
             return list2;
         if (list2 == NULL)
             return list1;

         ListNode *p1 = list1;
         ListNode *p2 = list2;
         ListNode *dummy = new ListNode();
         ListNode *p = dummy;
         while (p1 != NULL && p2 != NULL) {
             if (p1->val <= p2->val) {
                 p->next = p1;
                 p1 = p1->next;
             } else {
                 p->next = p2;
                 p2 = p2->next;
             }
             p = p->next;
         }

         while (p1 != NULL) {
             p->next = p1;
             p = p->next;
             p1 = p1->next;
         }

         while (p2 != NULL) {
             p->next = p2;
             p = p->next;
             p2 = p2->next;
         }
         return dummy->next;
     }