Sliding Window / Dynamic Coverage / Pointer Choreography
This category focuses on dynamic windows that breathe: expanding, contracting, aligning to chunk boundaries, and preserving invariants while the window glides through the input.
Let the right edge inject new characters into the substring, and whenever a repeat appears, watch the left edge sweep just far enough to restore uniqueness.
Watch the live window grow until its sum reaches the target, then contract immediately to squeeze out the smallest valid answer.
Build a live coverage window over s, track exactly when each required character count from t becomes satisfied, then tighten the window until it is as short as possible.
Split the source string into offset-aligned word chunks, run one sliding window per lane, and watch valid concatenation starts appear whenever the word multiset matches exactly.