Encode and Decode Strings medium

Problem Statement

Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.

Please note: The encoded string will be sent over the network, it thus must be a single string. The length of each string in the list will not exceed 100. Each string will contain only lowercase letters, and the list will contain at most 100 strings.

Example 1

Input: ["lint","code","love","you"]

Output: "lint,code,love,you" (Any valid serialization would be fine too.)

Example 2

Input: ["we","say","yes"]

Output: "we,say,yes"

Steps

1. Encoding: We need a delimiter to separate strings in the encoded string. A simple comma (,) works well. We concatenate all strings with the comma as a separator.
2. Decoding: We split the encoded string using the comma as a delimiter. This gives us a list of strings.

Explanation

The key to this problem is choosing a delimiter that will not appear within the input strings. Since the input strings only contain lowercase letters, a comma is a safe choice. More robust solutions might use a less common character or escape sequences to handle potential delimiter conflicts. However, given the problem constraints, a simple comma delimiter is sufficient and efficient.

Code

class Codec:
    def encode(self, strs):
        """Encodes a list of strings to a single string.
        :type strs: List[str]
        :rtype: str
        """
        return ','.join(strs)

    def decode(self, s):
        """Decodes a single string to a list of strings.
        :type s: str
        :rtype: List[str]
        """
        return s.split(',')

# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.decode(codec.encode(strs))

Complexity

• Time Complexity:
  • encode: O(N), where N is the total number of characters in all strings (linear time to concatenate).
  • decode: O(N), where N is the total number of characters in the encoded string (linear time to split).
• Space Complexity:
  • encode: O(N), where N is the total number of characters in all strings (space to store the concatenated string). Note that the space used by the input list is not considered part of our algorithm's space complexity.
  • decode: O(N), where N is the total number of characters in the encoded string (space to store the resulting list of strings). Similarly, input string's space is not considered.

This solution is efficient because it leverages Python's built-in join and split methods, which are optimized for string manipulation. The linear time complexity is optimal for this problem, given that we must process each character in the input and output strings at least once.