Encode and Decode Strings LeetCode Problem 271 [Python Solution]

The problem at hand, Encode and Decode Strings LeetCode Problem 271, is to design an algorithm that can encode a list of strings into a single string, which can then be sent over the network.

Additionally, we need to decode this string back into the original list of strings.

This LeetCode problem presents an interesting challenge due to the fact that the input strings can contain any character, not limited to just lowercase letters.

Let’s dive into the solution.

Understanding Delimiter Constraints

The key challenge here is how to differentiate between individual strings in the encoded format. We need a delimiter that separates one string from another.

However, this delimiter cannot be a random character, as it might appear within the strings themselves.

To address this, we’ll use a specific approach: for each string, we’ll start with an integer representing its length, followed by a delimiter (in this case, a pound sign #), and then the string itself.

This structure will help us accurately decode the strings.

For example, if we have the word “code” and want to encode it, the result would be “4#code”. The number 4 represents the length of the string, and the pound sign acts as a separator.

This approach ensures that even if the string contains numbers or special characters, we can still determine the length of each string.

Encode Function

Let’s start with the encode function, which takes a list of strings as input and encodes them into a single string.

def encode(self, strs):
    result = ""
    for s in strs:
        result += str(len(s)) + '#' + s
    return result

In this function, we iterate through each string in the input list.

For each string, we add its length, followed by a pound sign (#), and then the string itself to the result.

This process is repeated for all the strings.

Decode Function

Now, let’s implement the decode function, which takes an encoded string as input and decodes it into a list of strings.

def decode(self, s):
    result = []
    i = 0

    while i < len(s):
        j = i
        while s[j] != '#':
            j += 1
        length = int(s[i:j])
        i = j + 1
        j = i + length
        result.append(s[i:j])
        i = j

    return result

Encode and Decode Strings LeetCode Problem Python Code Solution

def encode(self, strs):
    result = ""
    for s in strs:
        result += str(len(s)) + '#' + s
    return result

def decode(self, s):
    result = []
    i = 0

    while i < len(s):
        j = i
        while s[j] != '#':
            j += 1
        length = int(s[i:j])
        i = j + 1
        j = i + length
        result.append(s[i:j])
        i = j

    return result

Here’s how the decode function works:

1. We initialize an empty list, result, to store the decoded strings and a pointer i to keep track of our position in the input string.
2. We iterate through the string character by character.
3. For each word, we find the delimiter (#) to determine the length of the following word.
4. We transform the substring representing the length into an integer.
5. Then, we extract the actual word using the length information.
6. Finally, we append the decoded word to the result list, and update our pointer i to the next starting position.

This process continues until we’ve decoded all the strings in the input.

Time and Space Complexity

The time complexity for both the encode and decode functions is O(n), where n is the total number of characters in the list of strings. This is because we iterate through each character once.

The space complexity is also O(n) since we store the result as a new string in the encode function and as a list of strings in the decode function.

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Conclusion

In this blog post, we’ve tackled the LeetCode problem 271: Encode and Decode Strings.

We’ve learned how to encode a list of strings into a single string using a specific delimiter structure, and then decode it back into the original list of strings.

This solution ensures that even when input strings contain various characters, we can accurately decode and retrieve the original data.

If you have any questions, suggestions, or comments, please feel free to share them. You can also check out the problem on LintCode to practice it yourself.

Happy coding!