String

Text as a sequence.

A string is a sequence of characters like "hello". You can read individual characters by index, get its length, slice out substrings, and join strings together (concatenation).

• Indexing — s[0] is the first character.
• Concatenation — "foo" + "bar" → "foobar".
• Common ops — length, substring, search, split, replace, case conversion.

Immutability and building.

In many languages (Java, Python, C#) strings are immutable — every "modification" creates a new string. Repeated concatenation in a loop is therefore O(n²); use a mutable builder (StringBuilder, list + join) for O(n).

ASCII    1 byte per char
UTF-8    1–4 bytes per char (variable)
UTF-16   2 or 4 bytes (surrogate pairs)

"Length" can mean bytes, code units, or code points — a subtlety that bites with emoji and non-Latin scripts.

Interning, matching, and internals.

• String interning — pooling identical string literals so equal strings share one object, saving memory and enabling reference equality.
• Pattern matching — naive search is O(n·m); KMP, Rabin–Karp (rolling hash), and Boyer–Moore achieve better bounds.
• Ropes & gap buffers — specialized structures for very large or heavily-edited text (editors).
• Unicode correctness — normalization forms, grapheme clusters, and locale-aware comparison matter for real-world text handling.