23. Merge k Sorted Lists

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23. Merge k Sorted Lists

题目

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

解析

• 本题解题思路很多
• 使用堆make_heap,或者优先队列
• 使用堆，分治，归并等

class Solution_23 {
public:
	struct CompareListNode
	{
		bool operator()(ListNode* a, ListNode* b)
		{
			return a->val > b->val;
		}
	};
	
	ListNode* mergeKLists(vector<ListNode*>& lists) {

		ListNode* head = new ListNode(0);
		ListNode* cur = head;
		priority_queue<ListNode*, vector<ListNode*>,CompareListNode> head_que; //元素是struct，class时，比较函数也要用对应的类型  //对于算法类型的函数调用sort();cmp使用函数即可
		for (int i = 0; i < lists.size();i++)
		{
			if (lists[i]) //非空入堆
			{
				head_que.push(lists[i]); //建立堆
			}
		}

		while (head_que.size()>0)
		{
			ListNode* temp = head_que.top(); //取堆顶元素
			head_que.pop();
			cur->next = temp;
			cur = cur->next;

			if (temp->next)
			{
				head_que.push(temp->next);
			}
		}
		cur->next = NULL;
		return head->next;
	}
};

题目来源

• 23. Merge k Sorted Lists
• LeetCode 23： Merge K Sorted Lists