Date: 2026-06-06
Time: 16:16
This file implements LeetCode 1656 — Design an Ordered Stream. It solves the problem of buffering out-of-order inserts and releasing values only when a contiguous prefix is available — essentially a reordering buffer with a read pointer.
OrderedStreamA class with two methods:
_init_(self, n: int) — Allocates a fixed-size list of None values and initializes a pointer self.ptr at index 0. The list is pre-sized to n because IDs are 1-indexed and bounded by n.insert(self, idKey: int, value: str) -> List[str] — Places value at idKey - 1 (converting from 1-indexed to 0-indexed), then scans forward from self.ptr, collecting all non-None values into a result list. The pointer advances past every collected value and stays there for the next call.Monotonic pointer scan: The pointer only moves forward, never backward. Each element is visited by the pointer at most once across all insert calls, giving O(n) total pointer work amortized over n inserts.
Pre-allocated buffer with sentinel: Uses None as a sentinel to distinguish filled vs. unfilled slots. This avoids needing a separate "filled" set or bitmap.
Imports: Only List from typing — no external or project dependencies.
Imported by: design-an-ordered-stream/test_solution.py. The massive "Imported By" list in the prompt is an artifact of the repo's test infrastructure, not actual imports of this module.
1. Caller creates OrderedStream(n) — a buffer of n slots and a pointer at 0.
2. Each insert(idKey, value) writes to slot idKey - 1.
3. The while loop drains all contiguous non-None slots starting at self.ptr.
4. If the inserted slot is ahead of the pointer (gap exists), the loop body never executes and an empty list is returned.
5. If the inserted slot fills the gap the pointer was waiting on, the loop flushes all contiguous ready values.
self.ptr only increases. Every slot at index < self.ptr has been returned exactly once.idKey is inserted exactly once. If duplicates were inserted, the second write would silently overwrite — no guard against this.idKey - 1 is used everywhere. Valid idKey range is [1, n]; passing 0 or n+1 would be an out-of-bounds access.None. The code trusts that callers respect the LeetCode contract (valid idKey range, no duplicates). An out-of-range idKey would raise IndexError from the list access.
design-an-ordered-stream/test_solution.py — See what edge cases are tested (single element, reverse-order inserts, already-contiguous inserts)design-an-ordered-stream/review.md — The code review may note complexity analysis or alternative approachesamortized-pointer-analysis — Why the while loop is O(n) total across all calls despite appearing inside each insertdesign-compressed-string-iterator/solution.py:StringIterator — Another stateful iterator design in this repo, useful for comparing pointer-based patternsordered-stream-amortized-linear — Total pointer movement across all n insert calls is O(n), making each insert O(1) amortizedordered-stream-none-sentinel — None is the only sentinel value; inserting None as a value would break the contiguity scanordered-stream-no-input-validation — No bounds checking on idKey and no duplicate detection; the code relies entirely on the LeetCode contractordered-stream-pointer-monotonic — self.ptr never decreases; once a value is returned it is never returned again