LeetCode #271: Encode and Decode Strings

https://leetcode.com/problems/encode-and-decode-strings/

To solve this problem, we can concatenate all the strings in the input list into a single string, separated by a delimiter. However, we need to use a special encoding technique to handle edge cases where the strings in the input list contain the delimiter character. One such technique is to prefix each string with its length followed by a delimiter, so that we can parse the encoded string later on. To decode the encoded string, we can iterate through it and split it back into a list of strings using the length information stored in the prefixes.

Steps to solve the problem:

1. Create a class called “Codec”.
2. Define an “encode” method that takes a list of strings as input.
3. Use a list comprehension to generate a list of encoded strings, where each string is the length of the corresponding input string followed by a delimiter, followed by the input string itself.
4. Concatenate the list of encoded strings into a single string using the join() method.
5. Return the encoded string.
6. Define a “decode” method that takes an encoded string as input.
7. Create an empty list called “strs” to store the decoded strings.
8. Set the index “i” to 0.
9. Iterate through the encoded string using a while loop. Inside the loop:
10. Use the find() method to find the position of the first delimiter (“:”) after the current index.
11. Convert the substring between the current index and the position of the delimiter to an integer, which represents the length of the next input string.
12. Increment the index to skip over the delimiter and the length information.
13. Use the substring between the current index and the calculated end index to extract the next input string.
14. Append the extracted input string to the “strs” list.
15. Update the index to skip over the current input string.
16. Return the list of decoded strings.

Python Code: Here’s the corrected Python code to solve the Encode and Decode Strings problem:

class Codec:

    def encode(self, strs):
        # Encode each string by prefixing its length followed by a delimiter
        encoded = [f"{len(s)}:{s}" for s in strs]
        # Concatenate the encoded strings into a single string
        return ''.join(encoded)

    def decode(self, s):
        # Create an empty list to store the decoded strings
        strs = []
        i = 0
        # Iterate through the encoded string
        while i < len(s):
            # Find the position of the delimiter
            j = s.find(':', i)
            # Convert the length information to an integer
            length = int(s[i:j])
            # Extract the input string
            input_str = s[j+1:j+1+length]
            # Append the input string to the list of decoded strings
            strs.append(input_str)
            # Update the index to skip over the current input string
            i = j + 1 + length
        # Return the list of decoded strings
        return strs

Time and Space Complexity:

The time complexity of the encode method is O(n), where n is the total length of all the strings in the input list. This is because we need to iterate through the input list and generate the encoded strings.

The time complexity of the decode method is also O(n), where n is the length of the encoded string. This is because we need to iterate through the encoded string and extract