1. String Prefix Shifting (Prefix Sum / Difference Array)

Problem: You are given a string s of lowercase English letters and an integer array rolls. Each element k in the rolls array represents an operation where you must increment the first k characters of the string s by 1 alphabetically (e.g., 'a' becomes 'b', 'b' becomes 'c', and 'z' wraps around to 'a'). Return the final string after all operations in the rolls array are applied.

2. Basic Hash Map Implementation

Problem: An easy-level question heavily reliant on a Hash Map.

3. Subarray Permutation Check

Problem: You are given an array of size n which is a permutation of the numbers from 1 to n. For each number x from 1 to n, you need to output 1 if there exists a contiguous subarray that is a valid permutation of the numbers from 1 to x, and 0 otherwise. Return the result as a binary string or array.

Format: Instead of standard algorithmic questions, this round focuses on practical software engineering skills using an existing codebase.

Tasks: You will be given access to an existing repository and asked to either fix bugs, add new features, or make specific modifications to the existing project.