Caesar Cipher with Case Preservation

Onsite coding. Implement a Caesar cipher: shift each letter by a fixed amount, wrapping within A-Z and a-z separately and preserving case; leave non-letter characters (digits, symbols) unchanged. Follow-up: for very long strings (thousands of chars) the per-character `% 26` is repeated work and any given letter always maps to the same output, so precompute a 26-entry (or 52-entry) translation table once and index into it. Requirements Shift every alphabetic character by a fixed shift, wrapping within its own case band: A-Z wraps to A-Z, a-z wraps to a-z. Preserve case; leave non-letter characters (digits, punctuation, spaces) unchanged. Notes Per character: ('A' + (c - 'A' + shift) % 26) for uppercase, the analogous 'a' band for lowercase, passthrough otherwise. Normalize shift with shift % 26 (and handle negative shifts if decryption is in scope). Follow-up — long input: for thousands of characters, recomputing % 26 per character is redundant because every occurrence of a given letter maps to the same target. Precompute a fixed translation table once (26 entries per case band, or a full 256-entry byte map) and index into it per character — O(1) per char with no modulo in the hot loop. Mention that with a full byte/char lookup table the passthrough characters fall out for free (they map to themselves), simplifying the inner loop to a single array index. Preparation Write the modular version first, then refactor to a precomputed lookup table and articulate why it removes repeated work on long inputs. Cover edge cases in tests: shift larger than 26, negative shift, wrap at z/Z, and a mixed string with digits and symbols.