Minimum Window Substring: The Gold Standard Problem

Concepts: pyMinWindow, pyHaveNeed, pyVariableWindowAdvanced

Minimum Window Substring (LeetCode 76) is the problem that separates candidates who memorized patterns from candidates who understand them. It is the hardest problem that still has a clean O(n) solution. It combines variable-size windows with frequency map tracking and a subtle validity condition. At companies like Meta, Stripe, and Databricks, this problem or a direct variant of it appears regularly in senior DE loops. Here is the approach that interviewers love: the have/need (also called formed/required) framework. The have/need Framework Explained Given string s and string t, find the minimum-length contiguous substring of s that contains all characters of t (with their required frequencies). The naive approach: slide a window, maintain a frequency map, compare to the target map on eve