合併k個排序連結串列，返回合併後的排序連結串列。請分析和描述演算法的複雜度。

示例:

輸入:
[
 1->4->5,
 1->3->4,
 2->6
]
輸出: 1->1->2->3->4->4->5->6

C#程式碼

/**

• Definition for singly-linked list.

• public class ListNode {

• public int val;
  

• public ListNode next;
  

• public ListNode(int x) { val = x; }
  

• }
  */
  public class Solution {
  public ListNode MergeKLists(ListNode[] lists)
  {
  int index = 0;
  int count = lists.Length;
  int temp = 1;

   if (count == 0) return null;
  
   while (temp < count)
   {
       index = 0;
       while (index + temp < count)
       {
           lists[index] = MergeTwoList(lists[index], lists[index + temp]);
           index += temp * 2;
       }
       temp *= 2;
   }
   return lists[0];
  

  }

  public ListNode MergeTwoList(ListNode node1, ListNode node2)
  {
  Stack stack = new Stack();
  int val1, val2;
  while (node1 != null && node2 != null)
  {
  val1 = node1.val;
  val2 = node2.val;
  if (val1 <= val2)
  {
  stack.Push(val1);
  node1 = node1.next;
  }
  else
  {
  stack.Push(val2);
  node2 = node2.next;
  }
  }

   while (node1 != null)
   {
       val1 = node1.val;
       stack.Push(val1);
       node1 = node1.next;
   }
  
   while (node2 != null)
   {
       val2 = node2.val;
       stack.Push(val2);
       node2 = node2.next;
   }
  
   ListNode node = null;
   while (stack.Count > 0)
   {
       node = new ListNode() { val = stack.Pop(), next = node };
   }
   return node;
   
  

  }
  }