Task Ordering with Dependencies

Problem

Given a list of task names tasks and a list of dependency pairs dependencies, return a valid execution order of all tasks. Each dependency [a, b] means task a must be completed before task b. If no valid ordering exists because the dependency graph contains a cycle, return an empty list.

Constraints

• 1 <= len(tasks) <= 10^4
• 0 <= len(dependencies) <= 2 * 10^4
• Task names are unique strings
• Every dependency references task names present in tasks
• A dependency [a, b] means a -> b