CustomCC0-1.0#ct-p1-011400
Balanced Window Replacement
Summary
- •Phase 1 / two-pointers
- •Reasoning-first competitive programming drill
Problem Description
Given an array a, find the minimum length subarray to replace so that every value 1..k appears exactly n/k times in the final array.
How to read this problem in plain language:
- This is a Phase 1 reasoning drill focused on two-pointers.
- Typical lenses to test first: two-pointers, sliding-window, invariant.
- Constraints reminder: 1 <= n <= 2e5, k divides n
Mini examples for mental simulation:
1) Boundary example: Answer should be 0 when all counts already target.
2) Adversarial example: One value dominates frequency; window must absorb excess.
Lite-mode writing target:
- Write 1~2 observations that shrink the search space.
- Name one final algorithm and state target complexity explicitly.
- Validate with at least 2 edge cases and one hand simulation.
Constraints
- •1 <= n <= 2e5, k divides n
Analysis
Key Insight
Each pointer moves at most n steps. This step should reduce search space or formalize correctness. State why this insight changes your algorithm choice.
two-pointerssliding-windowinvariant