Bash脚本-斐波那契 [英] Bash Script - Fibonacci

问题描述

我试图制作一个可以计算输入数字的斐波那契的递归函数，以这种方式卡住我如何获取通过递归获得的值.

I was trying to make a recursive function that can calculate the Fibonacci of the enter number, by the way I got stuck on how to get the values obtained by the recursion.

#!/bin/bash

#Function - Fibonacci
fib()
{

  number=$1

  if (( number < 2 ))
    then
      (( tmp = number ))
  else
      ((--number))
      term1=$(fib $number)

      ((--number))
      term2=$(fib $number)

      (( tmp = $(( term1 + term2 )) )) #Problem is here

  fi

  (( result = $result + tmp ))
  return $result

}

#Main Program.
fib $1
  echo fib $1 = $?

有人可以帮助我吗?

推荐答案

您的代码有两个问题.您不能使用$?进行任何有用的算术运算，因为数字会在255处回绕.并且嵌入的$((...))根本没有用，因为您已经在双括号内的算术上下文中.

There are a couple of issues with your code. You cannot use $? for any useful arithmetic because the number wraps around at 255. And the embedded $((...)) is not useful at all -- you are already in arithmetic context inside the double parentheses.

#!/bin/bash

fib()
{
  local number term1 term2 # Avoid leaking to main scope
  number=$1
  if ((number < 2))
    then
      ((tmp=number))
  else
      ((--number))
      term1=$(fib "$number")
      ((--number))
      term2=$(fib "$number")
      ((tmp=term1+term2))
  fi
  ((result=result+tmp))
  printf '%s\n' "$result"
}

#Main Program.
fib "$1"   # Quote argument properly!

在((算术括号))中，您不需要在变量前面使用$；这是无害的，但您应该尝试保持一致.

Inside the (( arithmetic parentheses )) you don't need the $ in front of variables; it's harmless, but you should probably try to be consistent.

与任何幼稚的Fibonacci实现一样，这是非常低效的.在辅助函数中一次计算序列的开头，然后拉出最终结果并显示它会更聪明.

As with any naïve Fibonacci implementation, this is hugely inefficient. It would be smarter to calculate the head of the sequence once in a helper function, then pull the final result and display it.

#!/bin/bash

fib2() {
    local f
    ((f=$1+$2))
    printf '%i %i\n' "$f" "$1"
}

fib()
{
    local i j
    j=$1
    shift
    for((i=1; i<j; ++i)); do
        set -- $(fib2 ${1-1} ${2-0})
    done
    printf '%s\n' "${1-$i}"
}

#Main Program.
fib "$1"

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