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 PyPy3 (2.4.0) (judge verdict: Accepted)

import sys
def main():
    input = sys.stdin.readline
    N,K,Q=map(int, input().split())
    *A,=map(int, input().split())

    ans=10**10
    from heapq import heappop, heappush
    A.append(-1)
    for y in A:
        if y==-1: break
        c=[]
        t=[]
        for a in A:
            if a >= y:
                heappush(t, a)
            else:
                for _ in range(len(t)-(K-1)):
                    heappush(c, heappop(t))
                t=[]
        if len(c) < Q: continue
        x=[heappop(c) for _ in range(Q)][-1]
        ans = min(ans, x-y)
    print(ans)

if __name__ == '__main__':
    main()