java - 为什么我的 HashMap 没有被填充

Question

我的代码用于查找 100 以内的整数的阶乘。我正在使用 BigInteger，但我的问题是我的 HashMap 没有被填充。

public class FCTRL2 {   
static Map<Integer,BigInteger> list = new HashMap<Integer,BigInteger>();

  public static void main(String[] args){
        InputStreamReader read = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(read);
        int numberOfInput=0;
        String input=null;
        try {
            numberOfInput = Integer.parseInt(in.readLine());
        } catch (NumberFormatException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        while(numberOfInput > 0){
            try {
                input = in.readLine();
            } catch (NumberFormatException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            BigInteger inputBig = new BigInteger(input);
            **System.out.println(factorial(inputBig));** prints correct factorial
        **System.out.println(list.get(factorial(inputBig).intValue()));** prints null
            numberOfInput--;
        }
  }

  public static BigInteger factorial(BigInteger input){
    if(list.containsKey(input.intValue()))
        return list.get(input.intValue());

    if(input.equals(new BigInteger("1")))
        return new BigInteger("1");
    BigInteger output;
    output = input.multiply(factorial(input.subtract(new BigInteger("1"))));
    list.put(input.intValue(), output);
    return output;
  }

}

Answer 1

替换

System.out.println(list.get(factorial(inputBig).intValue()));

与

System.out.println(list.get(inputBig.intValue()));

因为您要在此处插入要映射的值:list.put(input.intValue(), output);