Generated by Codex with GPT 5.6 Sol High
MEDIUMArray, Greedy, MatrixThe input is a square matrix of integers. One operation chooses two cells that share an edge and reverses both signs. The operation may be repeated any number of times, and the goal is to make the matrix’s total sum as large as possible.
Continue ...Generated by Codex with GPT 5.6 Sol High
MEDIUMString, Recursion, SimulationThe problem defines a family of binary strings without asking us to construct them directly. It begins with S1 = "0". Each later string consists of three parts: the previous string, a middle 1, and a reversed copy of the previous string with every bit flipped.
Generated by Codex with GPT 5.6 Sol High
HARDArray, Dynamic Programming, Stack, Greedy, Monotonic StackStart with an array of zeros. One operation chooses any contiguous subarray and raises every value in it by one; the goal is to build target in as few operations as possible.
Generated by Codex with GPT 5.6 Sol High
MEDIUMHash Table, String, Bit Manipulation, Rolling Hash, Hash FunctionGiven a binary string s and a length k, determine whether every one of the $2^k$ possible binary strings of length k appears somewhere as a contiguous substring of s.
Generated by Codex with GPT 5.6 Sol High
MEDIUMArray, Stack, SimulationStarting with an empty stack, consume the stream 1, 2, ..., n in order and emit Push and Pop operations so the stack becomes exactly the strictly increasing array target—then stop immediately.
Generated by Codex with GPT 5.6 Sol High
MEDIUMHash Table, String, Sliding WindowGiven a string made only of a, b, and c, count every contiguous substring that contains all three characters at least once.
Generated by Codex with GPT 5.6 Sol High
MEDIUMArray, Binary SearchGiven a list of positive integers, choose one positive integer divisor. Divide every number by it, round each quotient up, and add the rounded values. The goal is to find the smallest divisor that makes this sum no greater than threshold.
Generated by Codex with GPT 5.6 Sol High
HARDArray, Binary Search, Dynamic Programming, SortingEach job has a start time, an end time, and a profit. The goal is to choose a set of jobs that do not overlap and earn as much total profit as possible. A job ending at time x is compatible with one starting at time x.
Generated by Codex with GPT 5.6 Sol High
MEDIUMDatabaseThe Transactions table contains one row per transaction: its country, whether it was approved or declined, its amount, and its date. The requested report has one row for every (calendar month, country) pair and six columns:
Generated by Codex with GPT 5.6 Sol High
HARDArray, Hash Table, Sliding Window, CountingGiven an integer array nums and an integer k, count the nonempty contiguous subarrays that contain exactly k distinct values.
The word exactly makes the counting awkward. A normal sliding window is good at enforcing a one-sided condition such as “no more than k distinct values”: once a window has too many, move its left edge until it is valid again. But a valid window with exactly k distinct values may have several valid starting positions, so adding one answer for each right edge would miss subarrays.