For L4 level. Interveiwer just probided the below example (it is pretty self explanatory). Initially the input had only singe curly braces (Eg: "file{1,2,3}.txt")\nFollow up: multiple curly braces (Eg: "{june,july}logs.{txt,gz}")\nA litt diff from [Brace Expansion](https://leetcode.com/problems/brace-expansion/) (Eg: "{a,b}{c,{d,e}}" -> ["acd", "ace", "bcd", "bce"])\n\n```"file{1,2,3}.txt" -> ["file1.txt", "file2.txt", "file3.txt"]\n"{june,july}logs" -> ["junelogs", "julylogs"]\n"file1.txt" -> ["file1.txt"]\n"logs{june,july}" -> ["logsjune","logsjuly"],\n"abcd}ef" -> []\n"abc{def" -> []\n"{june,july}logs.{txt,gz}" -> ["junelogs.txt", "junelogs.gz", "julylogs.txt", "julylogs.gz"]\n"{a,b}{c,{d,e}}" -> ["acd", "ace", "bcd", "bce"]\n```

For L4 level. Interveiwer just probided the below example (it is pretty self explanatory). Initially the input had only singe curly braces (Eg: "file{1,2,3}.txt