Top DSA Questions for Frontend Interviews

Showing 32 of 32 questions

1. 1.What should you know about Big O Notation?easy

   Always state time AND space complexity of your solution

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2. 2.What should you know about Big O Notation?easy

   Know complexities of common operations (array access, hash lookup, sort)

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3. 3.What should you know about Binary System & Bit Manipulation?easy

   Use n & (n - 1) to clear the lowest set bit

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4. 4.What should you know about Binary System & Bit Manipulation?easy

   XOR cancels pairs: a ^ a = 0, a ^ 0 = a

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5. 5.What should you know about Arrays?easy

   Arrays are great when you need index-based access

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6. 6.What should you know about Arrays?easy

   For frequent front operations, consider a deque or linked list

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7. 7.What should you know about Hash Tables?easy

   Hash maps often turn O(n²) brute force into O(n)

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8. 8.What should you know about Hash Tables?easy

   When you need "have I seen this before?", think hash set

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9. 9.What should you know about Stacks?easy

   When you see nested structures or matching pairs, think stack

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10. 10.What should you know about Stacks?easy

    DFS (depth-first search) can use explicit stack or recursion

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11. 11.What should you know about Queues?easy

    BFS = Queue, DFS = Stack (or recursion)

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12. 12.What should you know about Queues?easy

    BFS finds shortest path in UNWEIGHTED graphs

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13. 13.What should you know about Graphs?easy

    State graph representation first in your first 30 seconds

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14. 14.What should you know about Graphs?easy

    Start with BFS or DFS on brute structure before optimizing

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15. 15.What should you know about Trie (Prefix Tree)?easy

    Always start word problems by clarifying alphabet and case rules

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16. 16.What should you know about Trie (Prefix Tree)?easy

    If many strings exist and queries are prefixes, start with a trie

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17. 17.What should you know about Linked Lists?easy

    Draw the pointers! Visualize before coding

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18. 18.What should you know about Linked Lists?easy

    Use dummy head node to simplify edge cases

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19. 19.What should you know about Heaps & Priority Queues?medium

    Start by clarifying whether you need smallest-first or largest-first

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20. 20.What should you know about Heaps & Priority Queues?medium

    Explain why repeated global selection is exactly what heaps optimize

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21. 21.What should you know about Trees?medium

    Start with a DFS template before adding logic

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22. 22.What should you know about Trees?medium

    Use level-by-level reasoning for BFS questions

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23. 23.What should you know about Recursion?medium

    State the state of one recursive call before moving to the next

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24. 24.What should you know about Recursion?medium

    Write base case first, then recursion, then combine

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25. 25.What should you know about Sorting Algorithms?medium

    You rarely implement sort from scratch — but you MUST understand partition logic

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26. 26.What should you know about Sorting Algorithms?medium

    When you see intervals, pairs, or "closest/largest" — think sort first

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27. 27.What should you know about Sliding Window?medium

    When you see "contiguous subarray" or "substring" with an optimization goal, think sliding window

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28. 28.What should you know about Sliding Window?medium

    Ask yourself: is the window size fixed or variable? This determines your template

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29. 29.What should you know about Backtracking?hard

    Draw decision tree first; label "choose / skip" branches

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30. 30.What should you know about Backtracking?hard

    Track exactly what is part of current path state

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31. 31.What should you know about Dynamic Programming?hard

    Start by identifying the subproblem: what decision is being made at each step?

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32. 32.What should you know about Dynamic Programming?hard

    Write the brute-force recursive solution first, then add memoization, then convert to tabulation if needed

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