90 problems. 1 a day. Interview ready.

The goal is to stop thinking about syntax so you can start thinking in edge cases and constraints.

Most interviews open here. Build the habit of proving why one pass and a hash map are enough.

The highest-frequency medium pattern at FAANG. If you can state the window invariant out loud, the code writes itself.

Monotonic stack questions separate candidates who memorized from candidates who understand. Learn the 'pop while worse' template once, reuse it forever.

"Binary search on the answer" (Koko, drink queries) is a FAANG favorite because it tests whether you see monotonicity, not whether you memorized mid = (lo+hi)/2.

LRU Cache is one of the most-asked design questions at Amazon and Meta. Everything before it here is training for it.

Tree questions are the most common medium at Google. The trick is always the same: decide what each subtree must report upward.

Find Median from a Data Stream is a top-5 Amazon question. Greedy is easy to code and hard to justify — practice saying why the local choice is safe.

Number of Islands and Course Schedule are the two most-asked graph questions in the industry. BFS/DFS on a grid must become muscle memory.

DP is where offers are decided. Every problem here follows the same script: define the state, write the recurrence, pick the base case.

Finish strong. If you can whiteboard Trapping Rain Water three different ways (brute force, prefix arrays, two pointers), you are ready for any onsite.