Memoization Top Down DP in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the memo array for storing computed Fibonacci values.

DSA C

int memo[[1]];

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A10

B0

C1000

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative size for the array.

Using too small size causing out of bounds.

The memo array size should be large enough to store Fibonacci values up to the maximum input. 1000 is a common safe size.

2fill in blank

medium

Complete the code to initialize the memo array with -1 to indicate uncomputed values.

DSA C

for (int i = 0; i < n; i++) {
    memo[i] = [1];
}

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A-1

B0

C1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing with 0 which is a valid Fibonacci number.

Using positive numbers that can confuse computed and uncomputed states.

We use -1 to mark that the Fibonacci value for that index is not computed yet.

3fill in blank

hard

Fix the error in the memoization check to return the stored value if already computed.

DSA C

if (memo[n] != [1]) {
    return memo[n];
}

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A-1

B1

Cn

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 0 which is a valid Fibonacci number.

Checking for 1 which is also a valid Fibonacci number.

We check if memo[n] is not -1, meaning it is already computed, so we return it directly.

4fill in blank

hard

Fill both blanks to complete the recursive Fibonacci function with memoization.

DSA C

int fib(int n) {
    if (n <= 1) return n;
    if (memo[n] != -1) return memo[n];
    memo[n] = fib(n [1] 1) + fib(n [2] 2);
    return memo[n];
}

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A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or multiplication instead of subtraction for indices.

Using wrong operators causing wrong recursion.

We calculate fib(n-1) and fib(n-2) and add them to get fib(n).

5fill in blank

hard

Fill all three blanks to complete the memoization initialization and function call.

DSA C

for (int i = 0; i < [1]; i++) {
    memo[i] = [2];
}
int result = fib([3]);

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

An

B-1

C10

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing with 0 instead of -1.

Calling fib with 0 which returns trivial result.

Initialize memo for all n elements with -1, then call fib(10) to compute the 10th Fibonacci number.