time limit per test: 0.25 sec. memory limit per test: 65536 KB
input: standard output: standard
Inspired by a "Little Bishops" problem, Petya now wants to solve problem for rooks.
A rook is a piece used in the game of chess which is played on a board of square grids. A rook can only move horizontally and vertically from its current position and two rooks attack each other if one is on the path of the other.
Given two numbers n and k, your job is to determine the number of ways one can put k rooks on an n × n chessboard so that no two of them are in attacking positions.
The input file contains two integers n (1 ≤ n ≤ 10) and k (0 ≤ k ≤ n2).
Print a line containing the total number of ways one can put the given number of rooks on a chessboard of the given size so that no two of them are in attacking positions.
Little Chess Pieces Series, SPb IFMO 2003-2004 Authumn Training Sessions
Codeforces (c) Copyright 2010-2019 Mike Mirzayanov