String Processing

Parse, transform, or analyse character sequences using frequency maps, two pointers, or sliding windows.

Parse, transform, or analyse character sequences using frequency maps, two pointers, or sliding windows.

The character frequency map always reflects the exact counts for the portion of the string processed so far.

Mapping characters to counts reduces membership checks to O(1) frequency lookups rather than O(n) re-scans.

Combining frequency tracking with a sliding window handles variable-length substring constraints in a single O(n) pass.