Question

我试图在Ruby中实现Karatsuba乘法。

# takes two integer x and y and partition them to x=a+b and y=c+d
# example if x = 1234 a=12 and b=34
# recursively compute a*c,a*d,b*c and b*d
def mult (x,y)
    if len(x) == 1 && len(y) == 1
             return  x*y 
       elsif len(x) > 1 && len(y) > 1
             ab = partition(x)
             cd =  partition(y)
             return ab.product(cd).each{ |num| mult(num[0],num[1]) }
       end
end
#method for partitioning works fine..
def partition(number)
     number.divmod( 10**(len(number)/2) )
end
#method to find size of integer works fine...
def len(value)
    value.to_s.split("").compact.size
end

所以

的预期回报

 p mult(12,34) should be 3,4,6,8
 but is [[1, 3], [1, 4], [2, 3], [2, 4]]

而不是return x*y，当我在print "#{x*y}"中使用line no:3时，它会打印3,4,6,8。我无法理解mult方法为nil返回x*y的原因。

Answer 1

问题是错误的迭代器：

#              ⇓⇓⇓⇓    
ab.product(cd).each{ |num| mult(num[0],num[1]) }

你想要的是Enumerable#map而不是：

ab.product(cd).map { |num| mult(num[0], num[1]) }

旁注：您也无需明确调用return：

def mult (x,y)
  if len(x) == 1 && len(y) == 1
    x*y
  elsif len(x) > 1 && len(y) > 1
    ab = partition(x)
    cd = partition(y)
    ab.product(cd).map { |num| mult(num[0], num[1]) }
  else
    raise "We got a problem"
  end
end
#method for partitioning works fine..
def partition(number)
  number.divmod( 10**(len(number)/2) )
end
#method to find size of integer works fine...
def len(value)
  value.to_s.size
end

p mult 12, 34
#⇒ [3,4,6,8]

方法不返回Ruby中的期望值

1 个答案: