The problem involves decoding a string that follows a specific encoding rule: k[encoded_string], where the encoded_string inside the square brackets is repeated exactly k times. Your task is to decode the string and return the decoded string.

You're given a graph, and your task is to create a completely independent copy of it. Ensure the cloned graph has the same structure and node values as the original.

Design a key-value store that supports storing values with timestamps. You should be able to retrieve the latest value for a key that's less than or equal to a given timestamp.