LeetCode [271] Encode and Decode Strings

 271. 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 is decoded back to the original list of strings.

Machine 1 (sender) has the function:

string encode(vector<string> strs) {
  // ... your code
  return encoded_string;
}

Machine 2 (receiver) has the function:

vector<string> decode(string s) {
  //... your code
  return strs;
}

So Machine 1 does:

string encoded_string = encode(strs);

and Machine 2 does:

vector<string> strs2 = decode(encoded_string);

strs2 in Machine 2 should be the same as strs in Machine 1.

Implement the encode and decode methods.

 

Note:

• The string may contain any possible characters out of 256 valid ascii characters. Your algorithm should be generalized enough to work on any possible characters.
• Do not use class member/global/static variables to store states. Your encode and decode algorithms should be stateless.
• Do not rely on any library method such as eval or serialize methods. You should implement your own encode/decode algorithm.

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//C++: 92ms typedef unsigned char uchar; class Codec { public: // Encodes a list of strings to a single string. string encode(vector<string>& strs) { string ret; for(auto s:strs){ int i = 0, len = s.size(), cnt; while(i<len){ cnt = 1; uchar c = s[i++]; while(i<len && (uchar)s[i]==c && cnt<254){ i++; cnt++; } ret += (uchar)cnt; ret += c; } ret += (uchar)255; } return ret; } // Decodes a single string to a list of strings. vector<string> decode(string s) { vector<string> ret; string cur; int i=0, len = s.size(); while(i<len){ uchar c = s[i++]; if(c==(uchar)255){ ret.push_back(cur); cur.clear(); }else{ int cnt = c; c = s[i++]; for(int i=0; i<cnt; ++i) cur += c; } } return ret; } };

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public class Codec { // Encodes a list of strings to a single string. public String encode(List<String> strs) { StringBuilder sb = new StringBuilder(); for(String s : strs) { sb.append(s.length()).append('/').append(s); } return sb.toString(); } // Decodes a single string to a list of strings. public List<String> decode(String s) { List<String> ret = new ArrayList<String>(); int i = 0; while(i < s.length()) { int slash = s.indexOf('/', i); int size = Integer.valueOf(s.substring(i, slash)); i = slash + size + 1; ret.add(s.substring(slash + 1, i)); } return ret; } } // Your Codec object will be instantiated and called as such: // Codec codec = new Codec(); // codec.decode(codec.encode(strs));