Arrays, strings and hash maps interview questions

Quick facts

Recall the answer first, then tap Show to check.

• x in some_listShowHide

  Scans the list from the front, so it costs O(n) per check. A set or dict answers the same question in O(1) on average.

• Dict orderShowHide

  Since Python 3.7, a dict keeps keys in the order they were first inserted. Updating a value keeps its position.

• list.append costShowHide

  Amortized O(1): the list over-allocates, so most appends write into spare room and only the occasional one copies.

• hash(-1) in CPythonShowHide

  Returns -2, because -1 is reserved as an error signal inside CPython's C code. Every other small int hashes to itself.

• Kotlin HashMap vs LinkedHashMapShowHide

  mutableMapOf() returns a LinkedHashMap, which keeps insertion order; a plain HashMap does not promise any order.