Ruby Fibonacci算法 [英] Ruby Fibonacci algorithm

问题描述

以下是我编写的用于计算斐波那契数列中的值的方法:

The following is a method I wrote to calculate a value in the Fibonacci sequence:

def fib(n)

    if n == 0
        return 0
    end
    if n == 1
        return 1
    end

    if n >= 2
        return fib(n-1) + (fib(n-2))
    end

end

它可以一直工作到n = 14，但是之后我收到一条消息，说该程序花费了太长时间来响应(我正在使用repl.it).有人知道为什么会这样吗?

It works uptil n = 14, but after that I get a message saying the program is taking too long to respond (I'm using repl.it). Anyone know why this is happening?

推荐答案

天真斐波那契进行了大量重复计算-在fib(14) fib(4)中进行了多次计算.

Naive fibonacci makes a lot of repeat calculations - in fib(14) fib(4) is calculated many times.

您可以将备忘录添加到算法中以使其更快:

You can add memoization to your algorithm to make it a lot faster:

def fib(n, memo = {})
  if n == 0 || n == 1
    return n
  end
  memo[n] ||= fib(n-1, memo) + fib(n-2, memo)
end
fib 14
# => 377
fib 24
# => 46368
fib 124
# => 36726740705505779255899443

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