[英]functional programming: recursive loop output fibonacci sequence in scala
Learning functional programming using scala. 使用Scala学习函数式编程。 Came across this exercise.
进行了此练习。
Write a recursive function to get the nth Fibonacci number ( http://mng.bz/C29s ). 编写一个递归函数以获取第n个斐波那契数( http://mng.bz/C29s )。 The first two Fibonacci numbers are 0 and 1. The nth number is always the sum of the previous two—the sequence begins 0, 1, 1, 2, 3, 5. Your definition should use a local tail-recursive function.
前两个斐波那契数是0和1。第n个数字始终是前两个数之和-序列以0、1、1、2、3、5开头。您的定义应使用局部尾递归函数。
def fib(n: Int): Int
My answer computes n+1 values and returns the nth. 我的答案计算n + 1个值并返回第n个。 Can anyone show me a better implementation where the extra n+1th value is not computed?
谁能给我展示一个更好的实现,其中不计算额外的n + 1个值?
object patterns {
def fib(n : Int): Int = {
@annotation.tailrec
def go(n: Int, prev2: Int, prev: Int): Int =
if(n<=0) prev2
else go(n-1, prev, prev2+prev)
go(n, 0, 1)
}
}
In case anyone is interested, this is from the book functional programming in scala by Chiusano and Bjarnason. 如果有人感兴趣,这是Chiusano和Bjarnason在scala中编写的《函数编程》一书。 Exercise 2.1 Looking forward to the replies.
练习2.1期待答复。
I think this: 我认为这:
def fib2(n: Int): Int = {
if (n < 1) 0
else if (n < 2) 1
else {
@annotation.tailrec
def go(i: Int, prev2: Int, prev: Int): Int =
if (i == n) prev
else go(i + 1, prev, prev2 + prev)
go(2, 1, 1)
}
}
or using ByName param: 或使用ByName参数:
def fib3(n: Int): Int = {
@annotation.tailrec
def go(n: Int, prev2: Int, prev: => Int): Int =
// ^ ByName
if (n <= 0) prev2
else {
val p = prev
go(n - 1, p, prev2 + p)
}
go(n, 0, 1)
}
I like to use stream
to implement it. 我喜欢使用
stream
来实现它。 Because the code is shorter and easier to understand. 因为代码更短,更容易理解。
def fibo():Stream[Int] = {
def addRec(o1:Int,o2:Int):Stream[Int] = {
o1 #:: addRec(o2,o1 + o2)
}
addRec(1,1)
}
println(fibo().take(100).toList)
get the nth
is simple to call fibo.drop(n-1)(0)
获得
nth
很容易调用fibo.drop(n-1)(0)
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