Arrays and strings tasks

Arrays and strings tasks often combine simple iteration with one extra idea: two pointers, a frequency map, prefix state, stable partitioning, or normalization. Start with a brute-force baseline, then explain which repeated work the optimized pattern removes.

Trade-off: compare time, memory, and implementation complexity before committing to a structure or pattern.

On interviews: Interviewers expect clean edge cases: empty input, casing, Unicode assumptions, duplicates, sortedness, and whether output order must be preserved.

Common pitfalls: Do not optimize before locking the requirements. String indexing can be tricky with Unicode, and in-place array changes can violate immutability expectations in application code.

Checklist:

• Write brute force first.
• Identify repeated work.
• Clarify order and mutation.
• Test empty and duplicate cases.