My first instinct was a plain hashmap and I started going down that path before realizing setall() would be O(n) if you iterate every key.
Clarify the requirements: get(key) and setall(value) must both be O(1). Use a versioned approach where each key stores a timestamp/version and a value, and a global version tracks the last setall. For get, if the key's version is older than the global version, return the setall value; otherwise return the stored value.
Pro tip: Mention that this design uses lazy propagation to avoid updating all keys during setall, which is key to achieving O(1). Also, discuss trade-offs like memory overhead for versioning and how to handle missing keys.
Ask if keys are integers or strings, if setall should affect all existing keys or also future keys, and if there are memory constraints. Confirm that both operations must be strictly O(1).
Suggest storing each key's value along with a version number, and maintaining a global version and a global setall value. Explain that get compares versions to decide which value to return.
For set(key, value): store value and current global version. For get(key): if key's version equals global version, return stored value; else return global setall value. For setall(value): increment global version and update global setall value.
Show that each operation is O(1) time. Discuss edge cases: get on a non-existent key after setall, multiple setalls, and set after setall.
Mention memory overhead of storing versions, potential integer overflow of version counter, and alternative designs like using a timestamp or a separate map for setall.
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