Solution For Encode And Decode Strings
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.
Example:
Input: [“hello”,”world”] Output: “5#hello5#world”
Explanation:
The input list of strings is encoded as a single string where ‘#’ separates the length of the string and the actual string. So “hello” is represented as “5#hello” and “world” is represented as “5#world”. The two strings are then concatenated to form the final encoded string “5#hello5#world”.
Solution:
To solve this problem, we need to come up with an encoding scheme that allows us to represent each string in the input list as a single string. We can use the following encoding scheme:
- For each string, we will represent it as “length of string#string”. For example, the string “hello” can be represented as “5#hello”.
- To separate multiple encoded strings, we will use the “#” character.
Using this encoding scheme, we can encode each string in the input list as a single string and then concatenate all the encoded strings to form a single encoded string.
To decode the encoded string back to the original list of strings, we can use the following steps:
- Initialize an empty list to store the decoded strings.
- Split the encoded string into individual encoded strings using “#” as the separator.
- For each encoded string, split it into the length and the actual string using “#” as the separator.
- Convert the length from string to integer and extract the actual string.
- Append the actual string to the decoded string list.
- Return the decoded string list.
Let’s take a look at the Python code for both encoding and decoding:
class Codec:
def encode(self, strs: List[str]) -> str:
encoded_strs = []
for s in strs:
encoded_strs.append(str(len(s)) + “#” + s)
return “”.join(encoded_strs)
def decode(self, s: str) -> List[str]:
decoded_strs = []
i = 0
while i < len(s):
j = i
while s[j] != "#":
j += 1
length = int(s[i:j])
decoded_strs.append(s[j + 1:j + length + 1])
i = j + length + 1
return decoded_strs
In the encode function, we use a for loop to iterate over each string in the input list. For each string, we encode it and append the encoded string to a list. We then return the concatenated string formed by joining all the encoded strings together.
In the decode function, we use a while loop to iterate over each encoded string in the input string. We use a nested while loop to find the length of the encoded string by searching for the “#” character. Once we have the length, we extract the actual string and append it to a list. We then update the value of the loop variable i to the position of the next encoded string. Finally, we return the list of decoded strings.
Time Complexity:
The time complexity of both encoding and decoding functions is O(n), where n is the number of strings in the input list. This is because we need to iterate over each string in the input list and perform some constant-time operations for each string.
Space Complexity:
The space complexity of the encode function is O(n) because we need to store the encoded strings in a list. The space complexity of the decode function is also O(n) because we need to store the decoded strings in a list.
Step by Step Implementation For Encode And Decode Strings
public class Codec { // Encodes a list of strings to a single string. public String encode(Liststrs) { StringBuilder sb = new StringBuilder(); for (String str : strs) { sb.append(str.length()).append('/').append(str); } return sb.toString(); } // Decodes a single string to a list of strings. public List decode(String s) { List res = new ArrayList<>(); int i = 0; while (i < s.length()) { int slash = s.indexOf('/', i); int size = Integer.valueOf(s.substring(i, slash)); res.add(s.substring(slash + 1, slash + size + 1)); i = slash + size + 1; } return res; } }
def encode(s): """ Encodes a list of strings to a single string. :type s: List[str] :rtype: str """ # edge case if not s: return "" # initialize encoded string encoded = "" # encode each string in the list for string in s: # get the length of the string and convert it to a string length = str(len(string)) # add the length of the string and the string itself to the encoded string encoded += length + ":" + string return encoded def decode(encoded): """ Decodes a single string to a list of strings. :type encoded: str :rtype: List[str] """ # edge case if not encoded: return [] # initialize decoded list decoded = [] # initialize index i = 0 # while loop to decode the encoded string while i < len(encoded): # initialize length length = "" # get the length of the string while encoded[i] != ":": length += encoded[i] i += 1 # increment i to get to the start of the string i += 1 # get the string string = encoded[i:i+int(length)] # add the string to the decoded list decoded.append(string) # increment i to get to the start of the next string i += int(length) return decoded
// Encodes a list of strings to a single string. function encode(strings) { let encodedString = ''; for (let i = 0; i < strings.length; i++) { let currentString = strings[i]; encodedString += currentString.length + '#' + currentString; } return encodedString; } // Decodes a single string to a list of strings. function decode(encodedString) { let strings = []; let startIndex = 0; while (startIndex < encodedString.length) { let endIndex = encodedString.indexOf('#', startIndex); let stringLength = parseInt(encodedString.substring(startIndex, endIndex)); let currentString = encodedString.substring(endIndex + 1, endIndex + 1 + stringLength); strings.push(currentString); startIndex = endIndex + 1 + stringLength; } return strings; }
class Codec { public: // Encodes a list of strings to a single string. string encode(vector& strs) { string encoded = ""; for (string& str : strs) { encoded += to_string(str.size()) + '#' + str; } return encoded; } // Decodes a single string to a list of strings. vector decode(string s) { vector strs; int i = 0; while (i < s.size()) { int index = s.find('#', i); int len = stoi(s.substr(i, index - i)); strs.push_back(s.substr(index + 1, len)); i = index + len + 1; } return strs; } }; // Your Codec object will be instantiated and called as such: // Codec codec; // codec.decode(codec.encode(strs));
public class Codec { // Encodes a list of strings to a single string. public string encode(IListstrs) { // Corner case if (strs == null || strs.Count == 0) { return ""; } StringBuilder sb = new StringBuilder(); // Encode each string in the list foreach (string str in strs) { sb.Append(str.Length + "#" + str); } return sb.ToString(); } // Decodes a single string to a list of strings. public IList decode(string s) { // Corner case if (string.IsNullOrEmpty(s)) { return new List (); } IList res = new List (); int i = 0; while (i < s.Length) { // Get the length of the next string int j = i; while (j < s.Length && s[j] != '#') { j++; } int len = Int32.Parse(s.Substring(i, j - i)); // Get the next string res.Add(s.Substring(j + 1, len)); // Move to the next string i = j + len + 1; } return res; } } // Your Codec object will be instantiated and called as such: // Codec codec = new Codec(); // codec.decode(codec.encode(strs));