Recursion vs Iteration When Each Wins in DSA C - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the recursive function call itself.

DSA C

void countdown(int n) {
    if (n <= 0) {
        printf("Blastoff!\n");
        return;
    }
    printf("%d\n", n);
    countdown([1]);
}

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An * 2

Bn + 1

Cn - 1

Dn / 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n * 2 or n / 2 does not guarantee reaching zero.

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

2fill in blank

medium

Complete the iterative loop to count down from n to 1.

DSA C

void countdown_iter(int n) {
    for (int i = n; i > 0; [1]) {
        printf("%d\n", i);
    }
    printf("Blastoff!\n");
}

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Ai++

Bi--

Ci = i - 2

Di = i + 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using i++ causes an infinite loop.

Skipping by 2 may miss numbers.

The loop must decrease i by 1 each time to count down.

3fill in blank

hard

Fix the error in the recursive factorial function call.

DSA C

int factorial(int n) {
    if (n == 0) return 1;
    return n * factorial([1]);
}

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An - 1

Bn + 1

Cn

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n or 1 does not reduce the problem.

Factorial calls itself with n - 1 to reduce the problem size.

4fill in blank

hard

Fill both blanks to create a recursive Fibonacci function.

DSA C

int fibonacci(int n) {
    if (n <= 1) return n;
    return fibonacci([1]) + fibonacci([2]);
}

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An - 1

Bn + 1

Cn - 2

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n or wrong subtraction breaks the sequence.

Fibonacci is sum of fibonacci(n-1) and fibonacci(n-2).

5fill in blank

hard

Fill all three blanks to create an iterative Fibonacci sequence generator.

DSA C

void fibonacci_iter(int n) {
    int a = 0, b = 1, c;
    if (n == 0) {
        printf("%d\n", a);
        return;
    }
    printf("%d\n%d\n", a, b);
    for (int i = 2; i < [1]; [2]) {
        c = a + b;
        printf("%d\n", c);
        a = [3];
        b = c;
    }
}

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An

Bi++

Cb

Da + b

Attempts:

3 left

💡 Hint

Common Mistakes

Wrong loop condition causes incorrect sequence length.

Incorrect increment causes infinite loop.

Wrong variable update breaks sequence.

Loop runs while i < n, increments i, and updates a to previous b.