Lähetit

import sys
import math
import itertools
from collections import defaultdict
 
n, k = map(int, sys.stdin.readline().rstrip().split())
 
if k > 2*n - 2:
	print 0
	sys.exit()
 
def countways(diags, board):
	thisdiag = diags[0]
	y = min(thisdiag, n - 1)
	x = max(0, thisdiag - (n-1))
	tot = 0
	#print diags, x, y
	while y >= 0 and x < n:
		if board[x][y] == False:
			x += 1
			y -= 1
			continue
		elif len(diags) == 1 and board[x][y] == True:
			tot += 1
			x += 1
			y -= 1
			continue
		xnew = x
		ynew = y
		while ynew < n and xnew < n:
			board[xnew][ynew] = False
			xnew += 1
			ynew += 1
		else:
			tot += countways(diags[1:], board)
		xnew = x
		ynew = y
		while ynew < n and xnew < n:
			board[xnew][ynew] = True
			xnew += 1
			ynew += 1
		x += 1
		y -= 1
	return tot
 
board = [[True]*n for q in range(n)]#range(1,n+1) + list(reversed(range(1,n)))
	
alltot = 0
for t in itertools.combinations(range(2*n - 1), k):
	alltot += countways(t, board)
 
print alltot % (10**9 + 7)
'''
	di = diags[:]
	thistot = 1
	for i in t:
		thistot *= max(di[i], 1)
		k = i + 2
		while k < len(di):
			di[k] -= 1
			k += 2
	tot += thistot
'''
 
 
# 1 2 2 3 3 2 1 
 

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 7

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 8

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 9

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 12

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 14

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 15

Group: 3

Verdict: ACCEPTED