mediumLeetCode#hash-map#dynamic-array

Insert Delete GetRandom O(1)

Implement unique insert, delete, and uniform random selection in expected constant time.

The Runtime Theory TeamSeptember 25, 202625 min read

Solve it

Solving happens on the judge — come back and mark it done

Sample cases

ininsert(1), remove(2), insert(2), getRandom()

outreturned value belongs to {1,2}; each is equally likely

ininsert(1), remove(1), insert(1)

outtrue

instructure contains [4,8,9], getRandom()

outreturned value is one of {4,8,9}

Implement unique insert, delete, and uniform random selection in expected constant time.

A good solution should

State the invariant or decision rule that makes the approach correct.
Explain time and space costs in terms of input size and required output.
Handle empty, minimal, duplicate, and boundary-shaped inputs.

Reasoning prompt

Use an array plus value-to-index map. Delete by swapping with the final element and updating the moved value’s index.

Use the linked judge for the canonical challenge. The examples above are compact TRT checks; create additional tests around the boundary most likely to break your invariant.

One dispatch a week

The trace behind each problem, the tradeoff that explains it, and one technical dispatch per week — no noise.

One technical dispatch per week. No noise.

Not started

A good solution should

Reasoning prompt

More practice in this topic

One dispatch a week