Count Secured Strings

Problem Overview

• Given two lowercase passwords s (customer) and t (system), count subsequences of s that are lexicographically greater than t.
• Return the count modulo 1,000,000,007.
• Inputs: 1 <= |s| <= 1e5, 1 <= |t| <= 100; output: a single integer.
• Real-world context: security analysis comparing generated passwords.
• From Amazon interviews; a coding interview problem and interview question.