Tree vs Array vs Linked List When Hierarchy Matters in DSA C++ - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple array of integers.

DSA C++

int arr[5] = [1];

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A[1, 2, 3, 4, 5]

B{1, 2, 3, 4, 5}

C(1, 2, 3, 4, 5)

D<1, 2, 3, 4, 5>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or square brackets instead of curly braces.

Forgetting to use any braces.

The correct syntax to initialize an array in C++ uses curly braces {}.

2fill in blank

medium

Complete the code to create a linked list node struct with an integer value and a pointer to the next node.

DSA C++

struct Node {
    int data;
    [1] next;
};

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ANode&

Bint*

CNode*

DNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using reference & instead of pointer *.

Using int* instead of Node*.

The pointer to the next node must be of type Node* to link nodes.

3fill in blank

hard

Fix the error in the tree node constructor to initialize the value and set left and right children to nullptr.

DSA C++

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left([1]), right([2]) {}
};

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ANULL

Bnullptr

C0

DNULLPTR

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL instead of nullptr.

Using 0 which is less clear.

In modern C++, nullptr is used to represent a null pointer safely.

4fill in blank

hard

Fill both blanks to create a function that returns the number of children of a binary tree node.

DSA C++

int countChildren(TreeNode* node) {
    int count = 0;
    if (node->left [1] nullptr) count++;
    if (node->right [2] nullptr) count++;
    return count;
}

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A!=

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator which counts missing children.

Using greater or less than operators which are invalid for pointers.

We check if left or right child is not equal to nullptr to count existing children.

5fill in blank

hard

Fill all three blanks to create a function that builds a linked list from an array of integers.

DSA C++

Node* buildList(int arr[], int size) {
    if (size == 0) return [1];
    Node* head = new Node();
    head->data = arr[0];
    head->next = buildList(arr + 1, [2]);
    return [3];
}

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Anullptr

Bsize - 1

Chead

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Returning NULL instead of nullptr.

Passing wrong size in recursive call.

Returning wrong variable instead of head.

Return nullptr for empty list, reduce size by 1 for recursion, and return head node.