Hash Map vs Array vs Linked List for Lookup in DSA Python - Compare & Choose

Challenge - 5 Problems

❓ Predict Output

intermediate

Lookup time in an array

What is the output of the code showing the index lookup of value 7 in the array?

DSA Python

arr = [3, 5, 7, 9, 11]
index = -1
for i in range(len(arr)):
    if arr[i] == 7:
        index = i
        break
print(index)

A 3

B 1

C -1

D 2

💡 Hint

Look for the position where 7 appears in the list.

The value 7 is at index 2 in the array. The loop finds it and breaks, so index is 2.

❓ Predict Output

intermediate

Lookup time in a linked list

What is the output of the code that searches for value 4 in a linked list and prints the found node's value?

DSA Python

class Node:
    def __init__(self, val):
        self.val = val
        self.next = None

head = Node(1)
head.next = Node(3)
head.next.next = Node(4)
head.next.next.next = Node(5)

current = head
found_val = None
while current:
    if current.val == 4:
        found_val = current.val
        break
    current = current.next
print(found_val)

A 4

B None

C 3

D 5

💡 Hint

Traverse nodes until you find the value 4.

The linked list nodes are checked one by one. When the node with value 4 is found, it is printed.

🧠 Conceptual

advanced

Time complexity comparison for lookup

Which data structure offers the fastest average lookup time for a key among these options?

A Array (unsorted)

B Linked List

C Hash Map

D Array (sorted, binary search)

💡 Hint

Think about average time to find an element by key.

Hash maps provide average O(1) lookup time, faster than arrays or linked lists.

❓ Predict Output

advanced

Hash map lookup with collisions

What is the output of the code that simulates a simple hash map lookup with collisions?

DSA Python

hash_map = {0: 'apple', 1: 'banana', 2: 'cherry'}
key = 5
index = key % 3
result = hash_map.get(index, 'not found')
print(result)

A not found

B cherry

C banana

D apple

💡 Hint

Calculate key modulo size to find index.

Key 5 modulo 3 is 2, so the value at index 2 is 'cherry'.

🧠 Conceptual

expert

Choosing data structure for frequent lookups and insertions

Which data structure is best suited for frequent insertions and lookups by key with minimal time complexity?

A Hash Map

B Array

C Linked List

D Binary Search Tree

💡 Hint

Consider average time for both insert and lookup operations.

Hash maps provide average O(1) time for insertions and lookups, better than linked lists, arrays, or BSTs.