Smallest Window Containing All Features

Problem Statement

In computer vision, feature matching often requires finding the smallest region in an image that contains all required feature types.

Given a string features representing detected features in a scan line, and a string required containing all feature types that must be present, find the length of the smallest contiguous substring of features that contains all characters in required.

If no such window exists, return 0.

Applications

• Finding minimal bounding regions containing specific objects
• Video keyframe selection
• Region-of-interest detection

Constraints

• $1 \leq len(features) \leq 10^5$
• $1 \leq len(required) \leq 100$
• Strings contain uppercase and lowercase English letters