Recursive functions in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a recursive function that calculates the factorial of a number.

R Programming

factorial <- function(n) {
  if (n == 0) {
    return(1)
  } else {
    return(n * factorial([1]))
  }
}

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

An * 1

Bn + 1

Cn - 1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using 1 does not reduce the problem size.

The recursive call must reduce the number by 1 each time to reach the base case.

2fill in blank

medium

Complete the code to define a recursive function that computes the nth Fibonacci number.

R Programming

fibonacci <- function(n) {
  if (n <= 1) {
    return(n)
  } else {
    return(fibonacci([1]) + fibonacci(n - 2))
  }
}

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A1

Bn + 1

Cn - 2

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n - 2 for both calls is incorrect.

The Fibonacci sequence is defined as fib(n) = fib(n-1) + fib(n-2).

3fill in blank

hard

Fix the error in the recursive function that sums numbers from 1 to n.

R Programming

sum_to_n <- function(n) {
  if (n == 1) {
    return(1)
  } else {
    return(n + sum_to_n([1]))
  }
}

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An + 1

Bn - 1

C1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using 1 does not reduce the problem size.

The recursive call must reduce n by 1 to reach the base case.

4fill in blank

hard

Fill both blanks to create a recursive function that counts down from n to 1 and prints each number.

R Programming

countdown <- function(n) {
  if (n == 0) {
    return()
  }
  print([1])
  countdown([2])
}

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An

Bn - 1

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Printing n - 1 before the call changes the order.

Calling countdown with n + 1 causes infinite recursion.

The function prints the current number n, then calls itself with n - 1.

5fill in blank

hard

Fill all three blanks to define a recursive function that reverses a string.

R Programming

reverse_string <- function(s) {
  if (nchar(s) == 0) {
    return("")
  } else {
    return(paste0(substring(s, [1]), reverse_string(substring(s, [2], [3]))) )
  }
}

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Anchar(s)

B1

C2

Dnchar(s) - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using fixed numbers instead of nchar(s) causes errors.

Incorrect substring indices cause wrong output.

The function takes the last character (substring from nchar(s) to nchar(s)) and appends the reverse of the rest (substring from 1 to nchar(s)-1).

Here, the blanks represent the last character and the rest of the string.