104. Merge k Sorted Lists

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合并k个已排序的链表

LintCode链接

题目描述

合并k个已排序的链表

样例

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对于下面三个链表，输出-1->2->4->null
[
  2->4->null,
  null,
  -1->null
],

思路

对于写过归并排序的人来说，题目比较简单，思路就是从k个链表中，找到当前最小的元素，插入到返回的链表中，并从被选择的链表中删除这元素

代码

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class Solution {
public:
    /**
     * @param lists: a list of ListNode
     * @return: The head of one sorted list.
     */
    ListNode *mergeKLists(vector<ListNode *> &lists) {
		// write your code here
		ListNode *root = NULL, *back_node = NULL;

		while (true)
		{
			int min = std::numeric_limits<int>::max();
			vector<ListNode *>::iterator min_iter = lists.end();
			for (auto iter = lists.begin(); iter != lists.end(); ++iter)
			{
				ListNode *cur_node = *iter;
				if (cur_node != NULL && cur_node->val < min)
				{
					min = cur_node->val;
					min_iter = iter;
				}
			}

			if (min_iter == lists.end())
			{
				break;
			}

			ListNode *min_node = *min_iter;
			if (root == NULL)
			{
				root = min_node;
				back_node = min_node;
			}
			else
			{
				back_node->next = min_node;
				back_node = min_node;
			}

			*min_iter = min_node->next;
			min_node->next = NULL;
		}

		return root;
	}
};