Get Smallest String

Problem Overview

• Given a lowercase string, select exactly one non-empty substring and replace each character with its previous alphabet letter (a wraps to z) once.
• Input: string s; Output: the lexicographically smallest resulting string; constraint: 1 ≤ |s| ≤ 1e5.
• Domain: string manipulation and lexicographic ordering relevant to real-world text processing.
• Source: asked in Ibm interviews; a common coding interview problem and interview question.