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(0);
        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;
    }