利用Java编写24点小游戏的实例代码

package com.company;

import java.util.*;

/**
 * 24点小游戏
 * 游戏规则：系统自动生成4个1-10的随机整数，玩家通过加减乘除操作，得到结果为24，每个数字只能使用一次
 */
public class Game24Player {

 final String[] patterns = {"nnonnoo", "nnonono", "nnnoono", "nnnonoo",
   "nnnnooo"};
 final String ops = "+-*/^";//存储运算符

 String solution;//解题答案
 List<Integer> digits;

 public static void main(String[] args) {
  new Game24Player().play();
 }

 void play() {
  digits = getSolvableDigits();

  Scanner in = new Scanner(System.in);
  while (true) {
   System.out.println("24点小游戏：");
   System.out.print("使用以下数字得出24点: ");
   System.out.println(digits);
   System.out.println("tips:输入q退出游戏，输入s打印解法以及出下一道题");
   System.out.print("> ");

   String line = in.nextLine();//获取控制台下一行输入的内容
   if (line.equalsIgnoreCase("q")) {
    System.out.println("\nThanks for playing");
    return;
   }

   if (line.equalsIgnoreCase("s")) {
    System.out.println(solution);
    digits = getSolvableDigits();
    continue;
   }

   char[] entry = line.replaceAll("[^*+-/)(\\d]", "").toCharArray();

   try {
    validate(entry);

    if (evaluate(infixToPostfix(entry))) {
     System.out.println("\n恭喜你，回答正确，请继续下一轮 ");
     digits = getSolvableDigits();
    } else {
     System.out.println("\n答题错误，请重新答题");
    }

   } catch (Exception e) {
    System.out.printf("%n%s 请重新输入.%n", e.getMessage());
   }
  }
 }

 //判断玩家在控制台输入的内容是否正确
 void validate(char[] input) throws Exception {
  int total1 = 0, parens = 0, opsCount = 0;

  for (char c : input) {
   if (Character.isDigit(c))
    total1 += 1 << (c - '0') * 4;
   else if (c == '(')
    parens++;
   else if (c == ')')
    parens--;
   else if (ops.indexOf(c) != -1)
    opsCount++;
   if (parens < 0)
    throw new Exception("括号不匹配.");
  }

  if (parens != 0)
   throw new Exception("括号不匹配.");

  if (opsCount != 3)
   throw new Exception("错误输入.");

  int total2 = 0;
  for (int d : digits)
   total2 += 1 << d * 4;

  if (total1 != total2)
   throw new Exception("输入有误.");
 }

 boolean evaluate(char[] line) throws Exception {
  Stack<Float> s = new Stack<>();
  try {
   for (char c : line) {
    if ('0' <= c && c <= '9')
     s.push((float) c - '0');
    else
     s.push(applyOperator(s.pop(), s.pop(), c));
   }
  } catch (EmptyStackException e) {
   throw new Exception("输入无效，请重新输入.");
  }
  return (Math.abs(24 - s.peek()) < 0.001F);
 }

 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;
  }
 }

 //获取一组随机数
 List<Integer> randomDigits() {
  Random r = new Random();
  List<Integer> result = new ArrayList<>(4);
  for (int i = 0; i < 4; i++)
   result.add(r.nextInt(9) + 1);//添加4个1-10的随机数
  return result;
 }

 List<Integer> getSolvableDigits() {
  List<Integer> result;
  do {
   result = randomDigits();
  } while (!isSolvable(result));
  return result;
 }

 boolean isSolvable(List<Integer> digits) {
  Set<List<Integer>> dPerms = new HashSet<>(4 * 3 * 2);
  permute(digits, dPerms, 0);

  int total = 4 * 4 * 4;
  List<List<Integer>> oPerms = new ArrayList<>(total);
  permuteOperators(oPerms, 4, total);

  StringBuilder sb = new StringBuilder(4 + 3);

  for (String pattern : patterns) {
   char[] patternChars = pattern.toCharArray();

   for (List<Integer> dig : dPerms) {
    for (List<Integer> opr : oPerms) {

     int i = 0, j = 0;
     for (char c : patternChars) {
      if (c == 'n')
       sb.append(dig.get(i++));
      else
       sb.append(ops.charAt(opr.get(j++)));
     }

     String candidate = sb.toString();
     try {
      if (evaluate(candidate.toCharArray())) {
       solution = postfixToInfix(candidate);
       return true;
      }
     } catch (Exception ignored) {
     }
     sb.setLength(0);
    }
   }
  }
  return false;
 }

 String postfixToInfix(String postfix) {
  class Expression {
   String op, ex;
   int prec = 3;

   Expression(String e) {
    ex = e;
   }

   Expression(String e1, String e2, String o) {
    ex = String.format("%s %s %s", e1, o, e2);
    op = o;
    prec = ops.indexOf(o) / 2;
   }
  }

  Stack<Expression> expr = new Stack<>();

  for (char c : postfix.toCharArray()) {
   int idx = ops.indexOf(c);
   if (idx != -1) {

    Expression r = expr.pop();
    Expression l = expr.pop();

    int opPrec = idx / 2;

    if (l.prec < opPrec)
     l.ex = '(' + l.ex + ')';

    if (r.prec <= opPrec)
     r.ex = '(' + r.ex + ')';

    expr.push(new Expression(l.ex, r.ex, "" + c));
   } else {
    expr.push(new Expression("" + c));
   }
  }
  return expr.peek().ex;
 }

 char[] infixToPostfix(char[] infix) throws Exception {
  StringBuilder sb = new StringBuilder();
  Stack<Integer> s = new Stack<>();
  try {
   for (char c : infix) {
    int idx = ops.indexOf(c);
    if (idx != -1) {
     if (s.isEmpty())
      s.push(idx);
     else {
      while (!s.isEmpty()) {
       int prec2 = s.peek() / 2;
       int prec1 = idx / 2;
       if (prec2 >= prec1)
        sb.append(ops.charAt(s.pop()));
       else
        break;
      }
      s.push(idx);
     }
    } else if (c == '(') {
     s.push(-2);
    } else if (c == ')') {
     while (s.peek() != -2)
      sb.append(ops.charAt(s.pop()));
     s.pop();
    } else {
     sb.append(c);
    }
   }
   while (!s.isEmpty())
    sb.append(ops.charAt(s.pop()));

  } catch (EmptyStackException e) {
   throw new Exception("Invalid entry.");
  }
  return sb.toString().toCharArray();
 }

 void permute(List<Integer> lst, Set<List<Integer>> res, int k) {
  for (int i = k; i < lst.size(); i++) {
   Collections.swap(lst, i, k);
   permute(lst, res, k + 1);
   Collections.swap(lst, k, i);
  }
  if (k == lst.size())
   res.add(new ArrayList<>(lst));
 }

 void permuteOperators(List<List<Integer>> res, int n, int total) {
  for (int i = 0, npow = n * n; i < total; i++)
   res.add(Arrays.asList((i / npow), (i % npow) / n, i % n));
 }
}