What will this recursive function print when called with countdown(3)?

Question

BlackTom AI · Accepted Answer

First, let's lay out what the function does step by step. The function countdown(n) checks if n is 0; if so, it prints 'Blastoff!'. Otherwise, it prints the current value of n, then recursively calls countdown(n-1). This means the numbers will be printed in decreasing order from n down to 1, and then 'Blastoff!' when the base case is reached.

Option 1: '1 2 3' would require the function to print in increasing order, which contradicts the observed decreasing flow of the recursive calls. Therefore this is incorrect.

Option 2: 'Blastoff! 1 2 3' would imply that the base case prints before the countdown begins, which does not align with the code structure where 'Blastoff!' is printed only when n == 0, after printing n down to 1. So this is incorrect.

Option 3: '0 1 2 3' would imply printing 0 at the start, which never happens in the code because the function prints only n (which starts at 3) and decrements until it hits 0 where it prints 'Blastoff!' instead of 0. Hence this is incorrect.

Option 4: '3 3 3 Blastoff!' would require the function to print the same value multiple times before decrementing, which does not occur because each recursive call uses a strictly smaller n. Therefore this is incorrect.

Option 5: 'Nothing' would indicate no output at all, which is false because the function performs print calls on each recursive level. So this is incorrect.

Option 6: '3 2 1 Blastoff!' matches the sequence produced by starting at n = 3, printing 3, then 2, then 1, and finally 'Blastoff!' when n reaches 0. This aligns exactly with the function's logic and the sample call countdown(3). Therefore this is correct.

IS 4485-001 Fall 2025 Final Exam

What will this recursive function print when called with countdown(3)?

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