String

A generic string question needs clarification before an algorithm: are we searching, reversing, comparing, counting, or parsing; are characters ASCII, Unicode code points, or grapheme clusters; and is case significant? Many tasks use a linear scan with one or two indices. Palindrome checks compare inward pointers; anagrams use frequency counts; substring matching may need a window or KMP; construction should use a mutable builder or array of pieces rather than repeated immutable concatenation. In languages where a string is UTF-16, indexing may split surrogate pairs, so mention code-point-aware iteration when user-facing Unicode correctness matters. For a simple traversal, time is O(n) and extra space is O(1); frequency maps or rebuilt output add O(alphabet) or O(n) space. The professional answer makes the missing contract explicit instead of inventing it.