Find the longest substring that can be made uniform by replacing at most k characters.
A good solution should
- State the invariant or decision rule that makes the approach correct.
- Explain the time and space complexity in terms of the input sizes and required output.
- Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.
Reasoning prompt
A window is feasible when its length minus the most frequent character count is at most k. Explain whether a stale maximum affects correctness in the common linear method.
Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.