PrepArena

Campaign

Bug Hunt

12 hand-made levels in teaching order — from your first off-by-one to a two-bug boss. Each one teaches a pattern from the DSA notes.

0/12 fixed
Start level 1
  1. 1The Missing Last ElementYour first ticket: the cart total is always a bit too low.easyLoops
  2. 2Sum ZeroA teammate wrote the two-pointer version of Sum Zero, but it returns [0, 0] for some inputs.easyTwo pointers
  3. 3Anagram CheckerQA says "aaz" and "zza" are being reported as anagrams.easyFrequency counter
  4. 4Count Unique ValuesThe dashboard shows one fewer unique visitor than the database does.easyTwo pointers
  5. 5Best Weekly SalesThe "best k-day streak" widget breaks for stores that lose money every day.mediumSliding window
  6. 6Binary SearchSearch works for most items, but the last product in the catalog is never found.easyDivide & conquer
  7. 7Recursion Without a Floorfactorial(0) crashes the server with "Maximum call stack size exceeded".easyRecursion
  8. 8Bubble Sort Gives Up EarlyThe leaderboard is only "kind of" sorted — the top score is right, the rest are not.mediumSorting
  9. 9Insertion Sort Drops a CardAfter sorting, one value is duplicated and another is missing.mediumSorting
  10. 10Palindrome PointersThe validator says "racecar" and "abba" are not palindromes.easyTwo pointers
  11. 11Two Sum, Same Index TwicetwoSum([3, 2, 4], 6) returns [0, 0] — using the 3 twice.mediumHash map
  12. 12Boss: The "abba" Trapboss · 2 bugsBoss level — two bugs. The longest-unique-substring service is wrong for "abba" and for every string.hardSliding window