DSA Skill Check

15 questions20 minPass: 60%+25 XP on first pass

15 mixed questions across the core DSA topics. 20 minutes. Explanations after you submit.

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Question 1
What is the time complexity of searching for a value in an unsorted array?
O(1)O(log n)O(n)O(n²)
Question 2
What is the time complexity of this code?
```
i = 1
while i < n:
    i = i * 2
```
O(n)O(log n)O(n log n)O(1)
Question 3
Which data structure gives O(1) average-time lookups by key?
ArrayHash mapLinked listBinary search tree
Question 4
nums = [2, 7, 11, 15], target = 9. Which indices does Two Sum return? (format: 0,1)
Question 5
For which input is two-pointer pair search (opposite ends) directly applicable?
A sorted arrayA linked list in random orderA hash mapAn unsorted array with duplicates
Question 6
What is the length of the longest substring without repeating characters in "pwwkew"?
Question 7
Binary search requires the data to be…
UniqueSorted (or monotonic)Of even lengthStored in a linked list
Question 8
Which pointer technique detects a cycle in a linked list in O(1) extra space?
Two headsFast and slow pointersDummy nodeRecursion
Question 9Select all that apply
Which are valid parenthesis strings? (select all that apply)
(())()())((()
Question 10
For a stack, which operation removes the most recently added item?
poppoll from the frontdequeueshift
Question 11
Inorder traversal of a Binary Search Tree returns the values…
In insertion orderIn sorted (ascending) orderIn reverse orderLevel by level
Question 12
Which traversal uses a queue?
InorderPreorderLevel order (BFS)Postorder
Question 13
How many ways are there to climb 4 stairs taking 1 or 2 steps at a time?
Question 14Select all that apply
Which problems are typically solved with dynamic programming? (select all that apply)
Coin change (minimum coins)Longest common subsequenceReverse a linked listBinary search in a sorted array
Question 15
Every number in [4, 1, 2, 1, 2] appears twice except one. What does XOR-ing all of them give?