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.
Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMArray, Hash Table, Sliding Window, Prefix SumGiven a binary array nums and a nonnegative integer goal, count the nonempty contiguous subarrays whose elements add up to exactly goal.
Contiguous and exact are the important words. The same element may belong to many valid subarrays, and zeros create several subarrays with the same sum. For example, in [1, 0, 1, 0, 1], there are four different subarrays whose sum is 2.
Generated by Codex with GPT 5.6 Sol XHigh
HARDDesign, Segment Tree, Ordered SetA range module remembers which real-number intervals are currently being tracked. It must support three operations on half-open ranges [left, right):
The half-open convention matters: adjacent ranges such as [5, 8) and [8, 12) fit together without overlapping, while removing [8, 10) leaves the first range untouched. Operations may overlap in any order, so the data structure must combine additions, preserve removals, and answer queries against the latest state.
Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMArray, Linked List, Design, QueueThe task is to build a fixed-capacity first-in, first-out queue. It must support inserting at the rear, deleting from the front, reading both ends, and checking whether it is empty or full. An attempted insertion into a full queue and an attempted deletion from an empty queue must fail cleanly.
Continue ...Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMString, Dynamic Programming, Stack, GreedyThe input contains opening parentheses, closing parentheses, and asterisks. Each * may act as (, act as ), or disappear. The task is to decide whether some choice for every asterisk makes the whole string a valid parenthesis sequence.
Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMDatabaseThe Employee table stores each employee’s ID, name, department, and manager ID. The task is to return the names of employees who manage at least five other employees directly.
Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMTree, Binary Search Tree, Binary TreeGiven a binary search tree and a key, remove the node whose value equals the key and return the tree’s root. If the key is absent, the tree should remain unchanged. Every value is unique, so the binary-search-tree ordering identifies at most one node to delete.
Continue ...Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMTwo Pointers, StringThe input is an array of characters. It must be compressed in place by replacing each maximal run of equal characters with the character followed by the run length—except that a run of length one keeps only the character. A count with multiple digits is written one digit at a time. For example, a, a, b, c, c, c becomes the meaningful prefix a, 2, b, c, 3, so the method returns 5.
Generated by Codex with GPT 5.6 Sol XHigh
MEDIUMHash Table, String, Sliding WindowGiven a text string s and a shorter pattern string p, the task is to return every starting index in s where a substring is an anagram of p. An anagram may arrange the letters differently, but it must contain exactly the same characters with exactly the same frequencies. Overlapping matches count separately.