Task: 24 game


C++: #include <random>
#include <iostream>
#include <stack>
#include <set>
#include <string>
#include <functional>
using namespace std;

class RPNParse
{
public:
  stack<double> stk;
  multiset<int> digits;

  void op(function<double(double,double)> f)
  {
    if(stk.size() < 2)
      throw "Improperly written expression";
    int b = stk.top(); stk.pop();
    int a = stk.top(); stk.pop();
    stk.push(f(a, b));
  }

  void parse(char c)
  {
    if(c >= '0' && c <= '9')
    {
      stk.push(c - '0');
      digits.insert(c - '0');
    }
    else if(c == '+')
      op([](double a, double b) {return a+b;});
    else if(c == '-')
      op([](double a, double b) {return a-b;});
    else if(c == '*')
      op([](double a, double b) {return a*b;});
    else if(c == '/')
      op([](double a, double b) {return a/b;});
  }

  void parse(string s)
  {
    for(int i = 0; i < s.size(); ++i)
      parse(s[i]);
  }

  double getResult()
  {
    if(stk.size() != 1)
      throw "Improperly written expression";
    return stk.top();
  }
};

int main()
{
  random_device seed;
  mt19937 engine(seed());
  uniform_int_distribution<> distribution(1, 9);
  auto rnd = bind(distribution, engine);

  multiset<int> digits;
  cout << "Make 24 with the digits: ";
  for(int i = 0; i < 4; ++i)
  {
    int n = rnd();
    cout << " " << n;
    digits.insert(n);
  }
  cout << endl;

  RPNParse parser;

  try
  {
    string input;
    getline(cin, input);
    parser.parse(input);

    if(digits != parser.digits)
      cout << "Error: Not using the given digits" << endl;
    else
    {
      double r = parser.getResult();
      cout << "Result: " << r << endl;

      if(r > 23.999 && r < 24.001)
        cout << "Good job!" << endl;
      else
        cout << "Try again." << endl;
    }
  }
  catch(char* e)
  {
    cout << "Error: " << e << endl;
  }
  return 0;
}




Java: import java.util.*;

public class Game24 {
    static Random r = new Random();

    public static void main(String[] args) {

        int[] digits = randomDigits();
        Scanner in = new Scanner(System.in);

        System.out.print("Make 24 using these digits: ");
        System.out.println(Arrays.toString(digits));
        System.out.print("> ");

        Stack<Float> s = new Stack<>();
        long total = 0;
        for (char c : in.nextLine().toCharArray()) {
            if ('0' <= c && c <= '9') {
                int d = c - '0';
                total += (1 << (d * 5));
                s.push((float) d);
            } else if ("+/-*".indexOf(c) != -1) {
                s.push(applyOperator(s.pop(), s.pop(), c));
            }
        }
        if (tallyDigits(digits) != total)
            System.out.print("Not the same digits. ");
        else if (Math.abs(24 - s.peek()) < 0.001F)
            System.out.println("Correct!");
        else
            System.out.print("Not correct.");
    }

    static float applyOperator(float a, float b, char c) {
        switch (c) {
            case '+':
                return a + b;
            case '-':
                return b - a;
            case '*':
                return a * b;
            case '/':
                return b / a;
            default:
                return Float.NaN;
        }
    }

    static long tallyDigits(int[] a) {
        long total = 0;
        for (int i = 0; i < 4; i++)
            total += (1 << (a[i] * 5));
        return total;
    }

    static int[] randomDigits() {        
        int[] result = new int[4];
        for (int i = 0; i < 4; i++)
            result[i] = r.nextInt(9) + 1;
        return result;
    }
}