Encode and Decode Strings
Medium
Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and decoded back to the original list of strings.
- Encoding: Given a list of strings, encode it into a single string.
- Decoding: Given the encoded string from step 1, decode it back to the original list of strings.
For example, consider the following list of strings: ["lint", "code", "love", "you"]
Your encode function should transform this list into a single string. The exact format of the encoded string is up to you, but it must contain sufficient information to accurately reconstruct the original list of strings.
Your decode function should take the encoded string produced by your encode function and return the original list of strings: ["lint", "code", "love", "you"]
Important Considerations:
- How will you handle empty strings in the input list?
- How will you handle strings that contain special characters or delimiters?
- How will you ensure that the decoding process accurately reconstructs the original strings, regardless of their content or length?
Solution
Encode and Decode Strings
This problem requires encoding a list of strings into a single string and then decoding that single string back into the original list of strings. Let's explore different approaches to solve this.
Naive Approach
A simple way to encode the strings would be to concatenate them directly. However, this approach makes it impossible to determine where one string ends and the next begins during decoding.
Encoding: Join the strings directly using a delimiter. Decoding: Split the combined string using the delimiter.
The problem with this naive approach is handling strings that contain the delimiter itself. If a string has the delimiter character, then the decode function will fail, and produce incorrect results.
Optimal Approach
A more robust solution involves prefixing each string with its length followed by a delimiter. This way, during decoding, we can read the length, determine the substring, and extract it.
Encoding: For each string, prefix it with its length and a delimiter (e.g., length#string). Concatenate these encoded strings.
Decoding: Read the length, then extract the string of that length, and repeat.
Edge Cases
- Empty List: An empty list of strings should encode to an empty string or a specific marker.
- Empty Strings: Empty strings in the list should be handled correctly during both encoding and decoding.
- Long Strings: The length prefix should be able to handle very long strings without overflow issues (using appropriate data types).
- Delimiter in String: The delimiter choice is not critical in this approach since the length prefix handles this problem.
Code (Python)
class Codec:
def encode(self, strs):
res = ""
for s in strs:
res += str(len(s)) + "#" + s
return res
def decode(self, s):
res = []
i = 0
while i < len(s):
j = i
while s[j] != "#":
j += 1
length = int(s[i:j])
res.append(s[j+1: j+1+length])
i = j + 1 + length
return res
Complexity Analysis
- Time Complexity:
- Encoding: O(N), where N is the total number of characters across all strings.
- Decoding: O(N), where N is the total number of characters in the encoded string.
- Space Complexity:
- Encoding: O(1), excluding the space for the output string.
- Decoding: O(1), excluding the space for the output list of strings.
This approach handles empty strings, long strings, and the delimiter in the strings effectively. The time and space complexity are linear with respect to the input size, making it an efficient solution.
