Problem:
Score : 600 points

Problem Statement

You are given an integer sequence A of length N and an integer K.
You will perform the following operation on this sequence Q times:

Choose a contiguous subsequence of length K, then remove the smallest element among the K elements contained in the chosen subsequence (if there are multiple such elements, choose one of them as you like).

Let X and Y be the values of the largest and smallest element removed in the Q operations. You would like X-Y to be as small as possible.
Find the smallest possible value of X-Y when the Q operations are performed optimally.

Constraints

1 \leq N \leq 2000

1 \leq K \leq N

1 \leq Q \leq N-K+1

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K Q
A_1 A_2 ... A_N

Output

Print the smallest possible value of X-Y.

Sample Input 1

5 3 2
4 3 1 5 2

Sample Output 1

1

In the first operation, whichever contiguous subsequence of length 3 we choose, the minimum element in it is 1.
Thus, the first operation removes A_3=1 and now we have A=(4,3,5,2).
In the second operation, it is optimal to choose (A_2,A_3,A_4)=(3,5,2) as the contiguous subsequence of length 3 and remove A_4=2.
In this case, the largest element removed is 2, and the smallest is 1, so their difference is 2-1=1.

Sample Input 2

10 1 6
1 1 2 3 5 8 13 21 34 55

Sample Output 2

7

Sample Input 3

11 7 5
24979445 861648772 623690081 433933447 476190629 262703497 211047202 971407775 628894325 731963982 822804784

Sample Output 3

451211184

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Linq;//リストの使用
using System.Collections.Generic;
using System.Text;//テキストの高速出力に必要
class Program
{
	static void Main()
	{
		string[] input = Console.ReadLine().Split(' ');
		int n = int.Parse(input[0]);
		int k = int.Parse(input[1]);
    int q = int.Parse(input[2]);
		long[] nums = Array.ConvertAll(Console.ReadLine().Split(' '),long.Parse);
    long minNum = 0;
    long answer = long.MaxValue;
    int countMemo = 0;
    List<long> answerList = new List<long>();
    List<long> answerSubList = new List<long>();

    for(int i = 0; i < n; i++)//最小値の選択
    {
      minNum = nums[i];
      answerList.Clear();
      answerSubList.Clear();
      for(int j = 0; j < n; j++)
      {
        if(nums[j] >= minNum)
        {
          countMemo++;
          if(countMemo == k)
          {
            for(int l = 0; l < k; l++)
            {
              answerSubList.Add(nums[j-l]);
            }
          }else if(countMemo > k) answerSubList.Add(nums[j]);
        }else
        {
          if(countMemo >= k)
          {
            answerSubList.Sort((a, b) => a.CompareTo(b));
            for(int l = 0; l < answerSubList.Count()-k+1; l++)
            {
              answerList.Add(answerSubList[l]);
            }
          }
          answerSubList.Clear();
          countMemo = 0;
        }
      }
      if(countMemo >= k)
      {
        answerSubList.Sort((a, b) => a.CompareTo(b));
        for(int l = 0; l < answerSubList.Count()-k+1; l++)
        {
          answerList.Add(answerSubList[l]);
        }
      }
      if(answerList.Count() < q) continue;
      else
      {
        answerList.Sort((a, b) => a.CompareTo(b));
        answer = Math.Min(answer, answerList[q-1]-minNum);
      }
    }
    
		Console.WriteLine(answer);
	}
}