Description
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.
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.
Input
The input file contains two integers n (1 ≤ n ≤ 10) and k (0 ≤ k ≤ n2).
Output
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.
Sample Input
Input
4 4
Output
24
用数学知识 c(n,k)* c(n,k) * A(k,k)
#include <iostream> #include <cstdio> using namespace std; int Jiecheng(int x) { int sum = 1; for(int i = 1;i <= x; i++) sum *= i; return sum; } int main() { int n ,k; int sum; scanf("%d%d",&n,&k); if(n < k) { sum = 0; } else { sum = (Jiecheng(n)/Jiecheng(k)/Jiecheng(n - k))*(Jiecheng(n)/Jiecheng(k)/Jiecheng(n - k)) * Jiecheng(k); } printf("%d ",sum); }