#完整的代码和计算结果
在完成了先前课程的学习，深入理解24点游戏的算法之后，我们在本节将为你揭晓项目的完整代码和计算结果。
为了使用交互式Scala解释器，你可以在打开的终端中输入命令：
cd /usr/local/scala-2.11.7/bin/
scala
当出现scala>开始的命令行提示符时，就说明你已经成功进入解释器了。如下图所示。
综合前面的介绍，这里我们给出最终的24点游戏的代码：
import scala.collection.mutable.Stack
trait BinaryOp{
val op:String
def apply(expr1:String,expr2:String) = expr1 + op + expr2
def unapply(str:String) :Option[(String,String)] ={
val index=str indexOf (op)
if(index>0)
Some(str substring(0,index),str substring(index+1))
else None
}
}
class Rational (n:Int, d:Int) {
require(d!=0)
private val g =gcd (n.abs,d.abs)
val numer =n/g
val denom =d/g
override def toString = numer + "\\" +denom
def +(that:Rational) =
new Rational(
numer * that.denom + that.numer* denom,
denom * that.denom
)
def -(that:Rational) =
new Rational(
numer * that.denom - that.numer* denom,
denom * that.denom
)
def * (that:Rational) =
new Rational( numer * that.numer, denom * that.denom)
def / (that:Rational) =
new Rational( numer * that.denom, denom * that.numer)
def this(n:Int) = this(n,1)
private def gcd(a:Int,b:Int):Int =
if(b==0) a else gcd(b, a % b)
}
object Bracket{
def matchBracket(str:String):Option[(Int,Int)] ={
val left = str.indexOf('(')
if(left >=0) {
val stack = Stack[Char]()
val remaining = str substring (left+1)
var index=0
var right=0
for(c <-remaining if right==0){
index=index + 1
c match{
case '(' => stack push c
case ')' => if (stack isEmpty) right= left+index else stack pop
case _ =>
}
}
Some(left,right)
}else None
}
def apply(part1:String,expr:String,part2:String) =part1+ "(" + expr + ")"+ part2
def unapply(str:String) :Option[(String,String,String)] ={
Bracket.matchBracket(str) match{
case Some((left:Int,right:Int)) =>{
val part1 = if (left == 0) "" else str substring(0, left )
val expr = str substring(left + 1, right)
val part2 = if (right == (str length)-1) "" else str substring (right+1)
Some(part1, expr, part2)
}
case _ => None
}
}
}
object Multiply extends {val op="*"} with BinaryOp
object Divide extends {val op="/"} with BinaryOp
object Add extends {val op="+"} with BinaryOp
object Subtract extends {val op="-"} with BinaryOp
object Rational extends {val op="\\"} with BinaryOp
object Test extends App{
val templates=List(
"N*N-N+N",
"(N-N)*N*N",
"N*N+N*N",
"(N+N)*N*N",
"N*N*N*N",
"(N+N*N)*N",
"(N*N-N)*N",
"N*N+N+N",
"(N/N-N)*N",
"(N-(N-N))*N",
"N-(N-N-N)",
"N+N-(N-N)",
"N*(N/N-N)",
"(N-N*N)*N",
"N*(N-N)+N",
"N+N+N/N",
"(N-N)*(N-N)",
"N+N*N/N",
"N*N/(N-N)",
"(N+N)*(N+N)",
"(N-N)*N/N",
"N+(N+N)/N",
"N*N/(N+N)",
"(N+N)*N/N",
"(N*N+N)*N",
"(N*N-N)/N",
"(N/N+N)*N",
"N*N/N/N",
"N+N+N-N",
"N-(N-N)+N",
"N/(N-N/N)",
"N+(N-N)*N",
"(N+N+N)*N",
"N+N*N-N",
"N*N-N/N",
"(N+N)*N-N",
"(N+N)*(N-N)",
"(N-N/N)*N",
"N*(N+N)+N",
"N*N+N/N",
"N*N/N-N",
"(N+N/N)*N",
"N*N*N/N",
"(N+N*N)/N",
"N+N*N+N",
"N-(N-N)*N",
"(N-(N+N))*N",
"N*N-N-N",
"N+N/N+N",
"(N-N)*N-N",
"(N+N)/N+N",
"N*N+N-N",
"N/N+N+N",
"N*N*N-N",
"(N*N+N)/N",
"N+N+N*N",
"N*(N-N)/N",
"N/N*N+N",
"N+N*N*N",
"N+N+N+N",
"N*N/(N*N)",
"N+(N+N)*N",
"(N-N)*N+N",
"(N+N+N)/N",
"(N+N)*N+N",
"N*N*N+N",
"N*N-(N-N)",
"N*N-(N+N)",
"(N-N-N)*N",
"N*N/N+N",
"(N+N-N)*N",
"N/(N/N-N)",
"N*N-N*N"
)
def eval(str:String):Rational = {
str match {
case Bracket(part1, expr, part2) => eval(part1 + eval(expr) + part2)
case Add(expr1, expr2) => eval(expr1) + eval(expr2)
case Subtract(expr1, expr2) => eval(expr1) - eval(expr2)
case Multiply(expr1, expr2) => eval(expr1) * eval(expr2)
case Divide(expr1, expr2) => eval(expr1) / eval(expr2)
case "" => new Rational(0, 1)
case Rational(expr1, expr2) => new Rational(expr1.trim toInt, expr2.trim toInt)
case _ => new Rational(str.trim toInt, 1)
}
}
def calculate(template:String,numbers:List[Int])={
val values=template.split('N')
var expression=""
for(i <- 0 to 3) expression=expression+values(i) + numbers(i)
if (values.length==5) expression=expression+values(4)
(expression,template,eval(expression))
}
def cal24(input:List[Int])={
var found = false
for (template <- templates; list <- input.permutations ) {
try {
val (expression, tp, result) = calculate(template, list)
if (result.numer == 24 && result.denom == 1) {
println(input + ":" + tp + ":" + expression)
found = true
}
} catch {
case e:Throwable=>
}
}
if (!found) {
println(input+":"+"no result")
}
}
def cal24once(input:List[Int])={
var found = false
for (template <- templates; list <- input.permutations if(!found)) {
try {
val (expression, tp, result) = calculate(template, list)
if (result.numer == 24 && result.denom == 1) {
println(input + ":" + tp + ":" + expression)
found = true
}
} catch {
case e:Throwable=>
}
}
if (!found) {
println(input+":"+"no result")
}
}
println(cal24once(List(5,5,5,1)))
}
下面给出所有从1到10的四个数字有解的结果：
前面我们给出了计算24的算法，这并非是计算24的Scala的最短的代码。除了之前“算法部分（一）”章节提到的方法，在Scala中，我们还可以使用更简单的方法来计算表达式——Scala 2.10.0之后的版本新增了字符串插值的功能。
比如：
scala> val name = "James"
name: String = James
scala> println(s"Hello, $name")
Hello, James
在字符串前使用“s”，可以将字符串中包含的字符串变量$var计算之后，再插入到最终的字符串中，比如本例中的$name。
同样，你可以可以使用表达式，比如：
scala> println(s" ${(4.0/10+2)*10}")
24.0
你可以在${}使用任意的表示式。如果你有兴趣的话，可以自行实现更简洁的24点算法或者对本课程提供的代码进行优化。
至此，使用Scala制作24点游戏的内容就全部完成了。回顾一下整个项目，我们先是介绍了如何计算表达式，然后用常见的算法计算24，其中还对List类型进行了详细讲解；接着，我们实现了全排列和穷举可能的表达式。综合上述内容后，最终通过Scala语言，设计和实现出了24点游戏。
下一节，我们将讲解一个拓展的知识点——如何在Java中调用Scala函数。建议有Java编程基础的同学继续学习这部分的内容。