快学Scala习题答案（第12章高阶函数）

object exc12 {  def main(args: Array[String]){    //1    def values(f:Int=>Int, low:Int , high:Int)={      //for(x <- low to high )yield x->f(x)      (low to high).map(x=>x->f(x))    }    println(values( x=>x*x, -5,5))    //2    assert( Array(2,13,5,12).reduceLeft(Math.max) == 13 )    //3    def factorial(x:Int)= (1 to x).reduceLeft(_*_)//(1 to x).product    assert( factorial(4) == 24 )    //4    println( 1 to -3)//Range()    def factorial2(x:Int)= (1 /: (1 to x))(_*_) //.foldLeft( 1)( _*_ )    assert( factorial2(0) == 1)    //5    def largest(f:Int=>Int, inputs:Seq[Int])={      inputs.reduceLeft( (x,y)=> {        if(f(x)>f(y)) f(x) else f(y)      }      )    }    println( largest(x=>10*x-x*x,1 to 10))// should be 25, why 9???    //6    def largest2(f:Int=>Int, inputs:Seq[Int])={      inputs.reduceLeft( (x,y)=> {        if(f(x)>f(y))          x        else          y} )    }    println( largest2(x=>10*x-x*x,1 to 10))//5    //7 **    def adjustToPair(f:(Int,Int)=>Int)={      tup:(Int,Int) => f(tup._1, tup._2)    }    println( adjustToPair(_*_)((6,7))==42)    println( ((1 to 10) zip (1 to 10)).map(adjustToPair(_+_)))        //8    println( Array("abc","a","1234").corresponds(Array(3,1,4))( (s:String,l:Int)=>if( s.size == l) true else false))    //10    def unless(condition: =>Boolean)(action: =>Unit ) ={      if( !condition ){        action      }    }    unless( 3 == 1){      println("not equals")    }  }}