Decode String

Problem You are given a string s that has been compressed according to the rule k[encoded_string]. This means that the substring inside the square brackets must be repeated exactly k times. The integer k is always positive. The input is guaranteed to be well‑formed: no extra spaces, square brackets are correctly nested and balanced, etc. Also, digits appear only as the repeat multiplier k; the original, uncompressed data never contained numeric characters. For instance, you…