76. Minimum Window Substring

How to solve Minimum Window Substring (LeetCode 76): the approach in brief

The problem

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".

Pattern

Minimum Window Substring is a Sliding Window problem, in the Variable Size (Condition-Based) subpattern. The pattern covers fixed-size, variable-size, and character frequency matching window techniques

Master variable-size sliding window for condition-based problems like longest substring without repeating characters.

Approach outline

1. Use two pointers to create a window of letters in s, which would have all the characters from t.
2. Expand the right pointer until all the characters of t are covered.
3. Once all the characters are covered, move the left pointer and ensure that all the characters are still covered to minimize the subarray size.

Complexity

The reference solution runs in O(n) time and O(k) space.

Asked at

Minimum Window Substring has been reported in interviews at Adobe, Airbnb, Amazon, Apple, Bloomberg, ByteDance, Facebook, Goldman Sachs.