Challenge

  • 10 minutes

For this challenge, you need to improve an existing program by making it run faster. Try to write the programs on your own, even if you have to go back and check the examples that you used to practice. Then, compare your solution with the one we have in the next unit.

Concurrency in Go is a complex problem that you'll understand better when you practice. This challenge is just one idea of what you can do to practice.

Good luck!

Calculate Fibonacci numbers faster with concurrency

Use the following program to calculate Fibonacci numbers in a sequential way:

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func fib(number float64) float64 {
    x, y := 1.0, 1.0
    for i := 0; i < int(number); i++ {
        x, y = y, x+y
    }

    r := rand.Intn(3)
    time.Sleep(time.Duration(r) * time.Second)

    return x
}

func main() {
    start := time.Now()

    for i := 1; i < 15; i++ {
        n := fib(float64(i))
    fmt.Printf("Fib(%v): %v\n", i, n)
    }

    elapsed := time.Since(start)
    fmt.Printf("Done! It took %v seconds!\n", elapsed.Seconds())
}

You need to build two programs from this existing code:

  • An improved version where you implement concurrency. It should take a few seconds to finish (no more than 15 seconds), as it does now. You should use buffered channels.

  • Write a new version that calculates Fibonacci numbers until the user enters quit in the terminal by using the fmt.Scanf() function. If the user presses Enter, you should calculate a new Fibonacci number. In other words, you'll no longer have a loop from 1 to 10.

    Use two unbuffered channels: one to calculate the Fibonacci number and another that's waiting for the "quit" message from the user. You'll need to use the select statement.

Here's an example of the interaction with the program:

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1

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13
quit
Done calculating Fibonacci!
Done! It took 12.043196415 seconds!