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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;

namespace AtTest._600problems
{
    class ARC098_E
    {
        static void Main(string[] args)
        {
            Method(args);
        }

        static void Method(string[] args)
        {
            int[] nkq = ReadInts();
            int n = nkq[0];
            int k = nkq[1];
            int q = nkq[2];
            int[] array = ReadInts();

            int[][] valPos = new int[n][];
            for(int i = 0; i < n; i++)
            {
                valPos[i] = new int[2] { array[i], i };
            }
            Array.Sort(valPos, (a, b) => a[0] - b[0]);

            int res = int.MaxValue;
            for(int i = 0; i < n; i++)
            {
                bool[] exclude = new bool[n];

                int remain = 0;
                for(int j = 0; j < n; j++)
                {
                    if (array[j] < array[i]) remain = k;

                    if (remain > 0) exclude[j] = true;
                    remain--;
                }
                remain = 0;
                for (int j = n-1; j >=0; j--)
                {
                    if (array[j] < array[i]) remain = k;

                    if (remain > 0) exclude[j] = true;
                    remain--;
                }

                int now = 0;
                for(int j = 0; j < n; j++)
                {
                    if (exclude[valPos[j][1]]) continue;

                    now++;
                    if (now == q)
                    {
                        res = Min(res, valPos[j][0] - array[i]);
                        break;
                    }
                }
            }

            WriteLine(res);
        }

        private static string Read() { return ReadLine(); }
        private static char[] ReadChars() { return Array.ConvertAll(Read().Split(), a => a[0]); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}