Implement Prefix Search and Node Removal

This interview included two coding tasks: 1. Implement a prefix-search data structure for strings with two operations: `insert(word)` and `count_with_prefix(prefix)`. A follow-up asks how to make matching case-insensitive and how to normalize inputs by removing trailing digits with a regular expression before storing or querying. 2. Given the head of a singly linked list and a target value `x`, remove every node whose value equals `x` and return the new head.