백준 11050번(Java)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		int[] nums = Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
		
		int N = nums[0];
		int K = nums[1];
		
		// nCk = n! / k!(n-k)!
		System.out.println(factorial(N) / (factorial(N-K) * factorial(K)));
	}
	
	static int factorial(int N) {
		
		if(N <= 1) {
			return 1;
		}
		
		return N * factorial(N-1);
	}
}