Fibonacci Using Recursion in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the base case for Fibonacci recursion.

DSA Go

func fibonacci(n int) int {
    if n == [1] {
        return n
    }
    return fibonacci(n-1) + fibonacci(n-2)
}

Drag options to blanks, or click blank then click option'

A1

B-1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 as the base case instead of 0 or 1.

Returning a fixed number instead of n.

The base case for Fibonacci recursion is when n equals 0, returning 0.

2fill in blank

medium

Complete the code to add the second base case for Fibonacci recursion.

DSA Go

func fibonacci(n int) int {
    if n == 0 || n == [1] {
        return n
    }
    return fibonacci(n-1) + fibonacci(n-2)
}

Drag options to blanks, or click blank then click option'

A3

B2

C1

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 1 as the second base case.

Missing the second base case entirely.

The second base case is when n equals 1, returning 1.

3fill in blank

hard

Fix the error in the recursive call to correctly calculate Fibonacci numbers.

DSA Go

func fibonacci(n int) int {
    if n == 0 || n == 1 {
        return n
    }
    return fibonacci(n[1]1) + fibonacci(n-2)
}

Drag options to blanks, or click blank then click option'

A-

B*

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction in the recursive call.

Using multiplication or division which are incorrect here.

The recursive call should subtract 1 from n to get the previous Fibonacci number.

4fill in blank

hard

Fill both blanks to complete the recursive Fibonacci function with correct base cases.

DSA Go

func fibonacci(n int) int {
    if n == [1] || n == [2] {
        return n
    }
    return fibonacci(n-1) + fibonacci(n-2)
}

Drag options to blanks, or click blank then click option'

A0

B1

C2

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 as a base case.

Returning a fixed number instead of n.

The base cases for Fibonacci are n == 0 and n == 1, returning n in both cases.

5fill in blank

hard

Fill the blanks to create a map of Fibonacci numbers for 0 to 5 using recursion.

DSA Go

package main

import "fmt"

func main() {
    fibMap := map[int]int{}
    for i := 0; i <= [1]; i++ {
        fibMap[i] = fibonacci([2])
    }
    fmt.Println(fibMap)
}

func fibonacci(n int) int {
    if n == 0 || n == 1 {
        return n
    }
    return fibonacci(n-1) + fibonacci(n-2)
}

Drag options to blanks, or click blank then click option'

A4

Bi

C5

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong upper bound in the loop.

Passing a fixed number instead of the loop variable to fibonacci.

The loop runs from 0 to 5, calling fibonacci(i) each time, and stores results in fibMap.

Practice

1. What does the Fibonacci sequence represent when calculated using recursion?

easy

A. Each number is the product of the two preceding numbers

B. Each number is the difference of the two preceding numbers

C. Each number is the sum of the two preceding numbers

D. Each number is the square of the previous number

Solution

1. Step 1: Understand Fibonacci sequence definition

   The Fibonacci sequence is defined such that each number is the sum of the two numbers before it.

2. Step 2: Relate to recursion

   Recursion calls the function for the two previous numbers and adds their results.

3. Final Answer:

   Each number is the sum of the two preceding numbers -> Option C

4. Quick Check:

   Fibonacci = sum of two previous numbers [OK]

Hint: Remember Fibonacci adds two previous numbers [OK]

Common Mistakes:

• Thinking Fibonacci multiplies previous numbers
• Confusing difference with sum
• Assuming Fibonacci squares previous number

2. Which of the following is the correct Go function signature for a recursive Fibonacci function?

easy

A. func fibonacci(n int) int

B. func fibonacci(n string) string

C. func fibonacci(n float64) float64

D. func fibonacci() int

Solution

1. Step 1: Identify parameter and return types

   The Fibonacci function takes an integer input and returns an integer output.

2. Step 2: Match correct Go syntax

   func fibonacci(n int) int matches the correct signature: func fibonacci(n int) int.

3. Final Answer:

   func fibonacci(n int) int -> Option A

4. Quick Check:

   Input and output are integers [OK]

Hint: Fibonacci uses int input and int output [OK]

Common Mistakes:

• Using string or float types incorrectly
• Omitting function parameters
• Wrong return type

3. What is the output of the following Go code?

func fibonacci(n int) int {
    if n <= 1 {
        return n
    }
    return fibonacci(n-1) + fibonacci(n-2)
}

func main() {
    fmt.Println(fibonacci(5))
}

medium

A. 5

B. 8

C. 3

D. 13

Solution

1. Step 1: Trace fibonacci(5) calls

   fibonacci(5) = fibonacci(4) + fibonacci(3), fibonacci(4) = 3, fibonacci(3) = 2, so total = 5.

2. Step 2: Calculate final value

   Sum of fibonacci(4) and fibonacci(3) is 3 + 2 = 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Fibonacci(5) = 5 [OK]

Hint: Recall Fibonacci(5) = 5 from sequence 0,1,1,2,3,5 [OK]

Common Mistakes:

• Confusing index starting at 0 or 1
• Adding wrong recursive results
• Miscounting base cases

4. Identify the error in this recursive Fibonacci function and select the fix:

func fibonacci(n int) int {
    if n == 0 {
        return 0
    } else if n == 1 {
        return 1
    }
    return fibonacci(n-1) - fibonacci(n-2)
}

medium

A. Add a loop instead of recursion

B. Change base case n == 0 to n == 2

C. Remove else if condition

D. Change '-' to '+' in the return statement

Solution

1. Step 1: Check recursive return operation

   The Fibonacci sequence sums previous two numbers, but code subtracts them.

2. Step 2: Correct the operation

   Replace '-' with '+' to correctly add fibonacci(n-1) and fibonacci(n-2).

3. Final Answer:

   Change '-' to '+' in the return statement -> Option D

4. Quick Check:

   Fibonacci sums previous two numbers [OK]

Hint: Fibonacci adds, never subtracts previous two numbers [OK]

Common Mistakes:

• Using subtraction instead of addition
• Changing base cases incorrectly
• Removing necessary conditions

5. How can you optimize the recursive Fibonacci function to avoid repeated calculations?

hard

A. Increase the recursion depth limit

B. Use memoization to store and reuse results

C. Use a global variable to count calls

D. Replace recursion with a random number generator

Solution

1. Step 1: Understand repeated calculations problem

   Recursive Fibonacci recalculates same values many times, causing inefficiency.

2. Step 2: Apply memoization technique

   Memoization stores results of previous calls to reuse them, reducing repeated work.

3. Final Answer:

   Use memoization to store and reuse results -> Option B

4. Quick Check:

   Memoization optimizes recursion by caching [OK]

Hint: Cache results to avoid repeated recursion calls [OK]

Common Mistakes:

• Increasing recursion depth does not fix inefficiency
• Counting calls doesn't optimize calculation
• Random numbers unrelated to Fibonacci