Implement encode/decode for list of strings

You are given a list of strings (may include digits and symbols). Implement two methods:

• encode(List<String> input) -> String: converts the list into a single encoded string.
• decode(String encoded) -> List<String>: converts the encoded string back into the original list.

Use the following encoding scheme: for each string s, append <len><s><sep> to the output, where <len> is the decimal length of s (number of characters), and <sep> is the character #.

Example:

Input: ["foo", "lis", "jljl", "12345678901"]

Lengths are 3, 3, 4, 11, so the encoded string is:

"3foo#3lis#4jljl#1112345678901#"

Implement both functions so that for any valid input list, decode(encode(input)) returns the original list.

Implement encode/decode for list of strings

Implement a serializer and deserializer for a list of strings. Write one function solution(mode, data):

• If mode == "encode", data is a list of strings and you must return one encoded string.
• If mode == "decode", data is an encoded string and you must return the original list.

Use this encoding rule for each string s: append str(len(s)) + s + "#" to the result. Here len(s) is the number of characters in s, and # is the record separator.

Example: ["foo", "lis", "jljl", "12345678901"] becomes "3foo#3lis#4jljl#1112345678901#".

Your implementation must satisfy solution("decode", solution("encode", arr)) == arr for every valid input.

Note: original strings may contain digits, spaces, and other symbols, but they will not contain #.

Constraints

• 0 <= number of strings <= 10^4
• The total number of characters across all input strings is at most 2 * 10^5
• Each original string may contain digits, spaces, and symbols, but it does not contain '#'
• For decode, the input string is guaranteed to be a valid encoding produced by the same scheme

Hints

1. When decoding, first find the next #. Everything before it belongs to exactly one encoded block.
2. If a block before # has total length m, and the length prefix has d digits, then the original string length must be m - d.