Was tun, wenn Sie eine (sehr) große Zahl speichern müssen?

Question

Ich versuche, ein Projekt Euler Problem zu tun, aber es beinhaltet die Ziffern einer sehr großen Zahl addieren. (100!)

Mit Java int und lange zu klein sind.

Vielen Dank für alle Anregungen

Answer 1

BigInteger Sieht aus wie es sein könnte, was Sie suchen.

Answer 2

Verwenden Sie BigInteger . Hier ist ein Beispiel aus dem Buch Java Beispiele in a Nutshell , die Rechen factorials, mit Caching beinhaltet.

import java.math.BigInteger;
import java.util.ArrayList;

/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or 
 * implied. You may study, use, and modify it for any non-commercial 
 * purpose. You may distribute it non-commercially as long as you 
 * retain this notice. For a commercial use license, or to purchase 
 * the book (recommended), visit 
 * http://www.davidflanagan.com/javaexamples2.
 */

/**
 * This program computes and displays the factorial of a number 
 * specified on the command line. It handles possible user input 
 * errors with try/catch.
 */
public class FactComputer {
  public static void main(String[] args) {
    // Try to compute a factorial.
    // If something goes wrong, handle it in the catch clause below.
    try {
      int x = Integer.parseInt(args[0]);
      System.out.println(x + "! = " + Factorial4.factorial(x));
    }
    // The user forgot to specify an argument.
    // Thrown if args[0] is undefined.
    catch (ArrayIndexOutOfBoundsException e) {
      System.out.println("You must specify an argument");
      System.out.println("Usage: java FactComputer <number>");
    }
    // The argument is not a number. Thrown by Integer.parseInt().
    catch (NumberFormatException e) {
      System.out.println("The argument you specify must be an integer");
    }
    // The argument is < 0. Thrown by Factorial4.factorial()
    catch (IllegalArgumentException e) {
      // Display the message sent by the factorial() method:
      System.out.println("Bad argument: " + e.getMessage());
    }
  }
}

/**
 * This version of the program uses arbitrary precision integers, so it 
 * does not have an upper-bound on the values it can compute. It uses an 
 * ArrayList object to cache computed values instead of a fixed-size 
 * array. An ArrayList is like an array, but can grow to any size. The 
 * factorial() method is declared "synchronized" so that it can be safely 
 * used in multi-threaded programs. Look up java.math.BigInteger and
 * java.util.ArrayList while studying this class.
 * Prior to Java 1.2, use Vector instead of ArrayList
 */

class Factorial4 {
  protected static ArrayList table = new ArrayList(); // create cache
  static { // Initialize the first element of the cache with !0 = 1.
    table.add(BigInteger.valueOf(1));
  }

  /** The factorial() method, using BigIntegers cached in a ArrayList */
  public static synchronized BigInteger factorial(int x) {
    if (x < 0)
      throw new IllegalArgumentException("x must be non-negative.");
    for (int size = table.size(); size <= x; size++) {
      BigInteger lastfact = (BigInteger) table.get(size - 1);
      BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(size));
      table.add(nextfact);
    }
    return (BigInteger) table.get(x);
  }

  /**
   * A simple main() method that we can use as a standalone test 
   * program for our factorial() method.
   */
  public static void main(String[] args) {
    for (int i = 0; i <= 50; i++)
      System.out.println(i + "! = " + factorial(i));
  }
}

Answer 3

java.lang.BigInteger oder java.lang.BigDecimal

Answer 4

import java.math.BigInteger;
import java.util.*;

public class Main {
    protected static ArrayList<BigInteger> table = new ArrayList<BigInteger>();

    static {
        table.add(BigInteger.valueOf(1));
    }

    public static synchronized BigInteger factorial(int x) {
        if (x < 0) throw new IllegalArgumentException("x must be non-negative.");
        for (int size = table.size(); size <= x; size++) {
            BigInteger lastfact = table.get(size - 1);
            BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(size));
            table.add(nextfact);
        }
        return table.get(x);
    }

    public static void main(String[] args) {
        for (int i = 0; i <= 50; i++)
            System.out.println(i + "! = " + factorial(i));
    }
}