IBM Coding Interview Questions

Showing 13 problems of 25

• #3mediumfrequently asked

  3. Longest Substring Without Repeating Characters

  Longest Substring Without Repeating Characters is IBM's sliding-window screener. The interviewer is grading whether you reach for the dynamic-window technique with a last-seen index map, whether you handle the 'jump the left pointer' optimization, and whether you ship O(n) with a single pass.

  3 free resourcesSolve →
• #15mediumfrequently asked

  15. 3Sum

  3Sum is IBM's two-pointer-on-sorted-array screener. The interviewer is grading whether you sort first to enable the two-pointer pattern, whether you skip duplicates cleanly at all three pointer positions, and whether you arrive at O(n^2) instead of the naive O(n^3).

  3 free resourcesSolve →
• #49mediumfrequently asked

  49. Group Anagrams

  Group Anagrams is IBM's hash-keyed-bucketing screener. The interviewer is grading whether you pick a canonical key (sort the chars OR a frequency tuple), articulate the tradeoff between O(k log k) sort and O(k) counter, and ship the bucket map cleanly.

  3 free resourcesSolve →
• #53mediumfrequently asked

  53. Maximum Subarray

  Maximum Subarray is IBM's Kadane's-algorithm screener. The interviewer is grading whether you can derive Kadane's by stating the 'extend-or-restart' decision rule, ship it in O(n) with O(1) space, and articulate how it generalizes to the 2D variant.

  4 free resourcesSolve →
• #56mediumfrequently asked

  56. Merge Intervals

  Merge Intervals is IBM's sort-then-sweep screener — directly relevant to calendar scheduling and time-range queries in IBM Cloud monitoring. The interviewer is grading whether you sort by start, whether you handle the touching-but-not-overlapping edge case, and whether you ship O(n log n) cleanly.

  3 free resourcesSolve →
• #102mediumfrequently asked

  102. Binary Tree Level Order Traversal

  Binary Tree Level Order Traversal is IBM's BFS-on-trees screener. The interviewer is grading whether you reach for an explicit queue, whether you use the queue-size snapshot trick to delimit levels, and whether you handle the empty-tree edge case cleanly.

  3 free resourcesSolve →
• #139mediumfrequently asked

  139. Word Break

  Word Break is IBM's DP-on-strings screener. The interviewer is grading whether you recognize the 'can-be-split' DP recurrence, whether you build the Set for O(1) word lookup, and whether you bound the inner loop by the maximum word length to avoid pathological inputs.

  3 free resourcesSolve →
• #146mediumcompany favorite

  146. LRU Cache

  LRU Cache is IBM's data-structure-design screener — relevant to IBM Cloud / DB2 / storage teams where eviction policies matter daily. The interviewer is grading whether you reach for hash map + doubly linked list together, articulate why neither suffices alone, and ship O(1) for both get and put.

  4 free resourcesSolve →
• #200mediumfrequently asked

  200. Number of Islands

  Number of Islands is IBM's graph-traversal screener — a 2D grid where each connected region of land cells counts as one island. The interviewer is grading whether you pick BFS or DFS deliberately, articulate the stack-depth risk on huge maps, and handle the in-place vs visited-set trade.

  3 free resourcesSolve →
• #207mediumfrequently asked

  207. Course Schedule

  Course Schedule is IBM's cycle-detection-in-directed-graph screener — directly relevant to dependency-graph problems in IBM Cloud orchestration and DB2 query planning. The interviewer is grading whether you reach for topological sort (Kahn's or DFS-coloring), whether you handle disconnected nodes, and whether you finish in O(V+E).

  4 free resourcesSolve →
• #215mediumfrequently asked

  215. Kth Largest Element in an Array

  Kth Largest Element is IBM's heap/quickselect screener. The interviewer is grading whether you ship the O(n log k) min-heap solution under time pressure, whether you mention Quickselect for O(n) average, and whether you handle the duplicate-friendly definition correctly.

  4 free resourcesSolve →
• #238mediumfrequently asked

  238. Product of Array Except Self

  Product of Array Except Self is IBM's prefix/suffix-array screener. The interviewer is grading whether you avoid the forbidden division operator, derive the two-pass left/right product technique, and ship it in O(1) extra space using the output array as your scratch.

  3 free resourcesSolve →
• #322mediumfrequently asked

  322. Coin Change

  Coin Change is IBM's unbounded-knapsack DP screener. The interviewer is grading whether you recognize the unbounded variant (each coin reusable), whether you ship the O(amount * coins) bottom-up DP, and whether you handle the impossible case (amount > 0 but no combination works) cleanly.

  3 free resourcesSolve →