Get Special String

Problem Overview

• Generate a special string (no two adjacent characters match) of the same length as s that is lexicographically greater than s; if multiple exist, return the smallest; if none, return "-1".
• Input: lowercase string s (1 ≤ |s| ≤ 10^6); Output: the special string or "-1"; no wrap-around after 'z'.
• Real-world context: text generation utility ensuring no adjacent repeats.
• From Amazon interviews; a coding interview problem and interview question.