long ans = 1;
for (int x = n, y = 1; y < m; ++x, ++y) {
    ans = ans * x / y;
}

// 
package com.rc;

import java.io.File;

public class DeleteFileJava {

    /**
     * 此类显示如何在Java中删除文件
     * @param args
     */
    public static void main(String[] args) {
        // 带路径的文件名
        File file = new File("tmp/tmp2/file.txt");
        if(file.delete()){
            System.out.println("tmp/tmp2/file.txt File deleted");
        }else System.out.println("File tmp/tmp2/file.txt doesn't exist");

        // 只提供文件名称
        file = new File("file.txt");
        if(file.delete()){
            System.out.println("file.txt File deleted from Project root directory");
        }else System.out.println("File file.txt doesn't exist in the project root directory");

        //relative path
        file = new File("temp/file.txt");
        if(file.delete()){
            System.out.println("temp/file.txt File deleted from Project root directory");
        }else System.out.println("File temp/file.txt doesn't exist in the project root directory");

        // 删除空的目录
        file = new File("temp");
        if(file.delete()){
            System.out.println("temp directory deleted from Project root directory");
        }else System.out.println("temp directory doesn't exist or not empty in the project root directory");

        // 试图删除非空目录
        file = new File("D:/user/maxsu/project");
        if(file.delete()){
            System.out.println("D:/user/maxsu/project directory deleted from Project root directory");
        }else System.out.println("D:/user/maxsu/project directory doesn't exist or not empty");
    }

}
//更多请阅读：https://www.yiibai.com/java/java-delete-file-directory.html

import java.io.File;

public class JavaDeleteDirectory {

    public static void main(String[] args) {
        File dir = new File("D:/worksp/java/log");

        if(dir.isDirectory() == false) {
            System.out.println("Not a directory. Do nothing");
            return;
        }
        File[] listFiles = dir.listFiles();
        for(File file : listFiles){
            System.out.println("Deleting "+file.getName());
            file.delete();
        }
        //现在目录为空，所以可以删除它
        System.out.println("Deleting Directory. Success = "+dir.delete());

    }

}
//更多请阅读：https://www.yiibai.com/java/java-delete-file-directory.html