[leetcode#271] Encode and Decode Strings

problem:

Design a algorithm to encode a list of strings to a string. The encoded string is then sent over the network and are 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);

strs2In Machine 2 should is the same as in Machine strs 1.

Implement the encode and decode methods.

Note:

• The string may contain any possible characters out of the valid ASCII characters. Your algorithm should is generalized enough to work on any possible characters.
• Don't use the class member/global/static variables to store states. Your encode and decode algorithms should be stateless.
• Rely on any library method such as eval or Serialize methods. You should implement your own Encode/decode algorithm.

Analysis:

This problem needs some skills in implementation. Once you know the tricky skill underlying it, you would think how it could is so easy!Instant Idea:can Some special characters to separate those strings. Nope! No matter what kind of special characters your use, it could appear in all individual string by chance!Then I had came up with the certain number of characters to record each string' s information in the overall string. However, how much prefix characters is enough? How to Sepearte the information forEach of the string out? that' s a headache problem!The genius idea:why not combinely use special character and size information. Wrap your string in following the encode string.encode_string=Size1:{original_string}size2:{original_string}size3:{original_string}size4:{original_string}each Original String is wrap through following way:original_string--->size1:{original_string}for a single block, how could we extract the orginal_string out of wraped string?Step1:get the start index of the block. Inital start Index is 0.-------------------------------------------------------------------intNext_start = 0; Step2:use ":" To get the orginal_string s length.-------------------------------------------------------------------intSplit_index = S.indexof (":", Next_start);intLen =integer.valueof (s.substring (Next_start, Split_index)); Step3:combinely use ":"and length information to extract the original string out.-------------------------------------------------------------------String Item= S.substring (split_index+1, split_index+1+len); Ret.add (item); Step4:update the start index forThe next string.-------------------------------------------------------------------Next_start= Split_index+1+len;

Wrong solution:

 Public classCodec {//encodes a list of strings to a single string.     PublicString Encode (list<string>STRs) {        if(STRs = =NULL)            Throw NewIllegalArgumentException ("STRs is null"); StringBuffer Buffer=NewStringBuffer ();  for(String str:strs) {buffer.append (Str.length ()); Buffer.append (":");        Buffer.append (str); }        returnbuffer.tostring (); }    //decodes a single string to a list of strings.     PublicList<string>Decode (String s) {List<String> ret =NewArraylist<string> (); intNext_start = 0; intSplit_index = S.indexof (":"); intLen =integer.valueof (s.substring (Next_start, Split_index));  while(Next_start <s.length ()) {String Item= S.substring (split_index+1, split_index+1+Len);            Ret.add (item); Next_start= split_index+1+Len; Split_index= S.indexof (":", Next_start); Len=integer.valueof (s.substring (Next_start, Split_index)); }        returnret; }}

MistakesAnalysis:

Last executed Input:[]mistake analysis:my first implementation are complex and so ugly!!!Since We need to DoThe same work forAll wrapped strings, we should don't allow a singly operation spill out the common block.intNext_start = 0;intSplit_index = S.indexof (":");//What if there was no string in the encoded string!!! This ugly logic incure a corner case!intLen =integer.valueof (s.substring (Next_start, Split_index)); while(Next_start <s.length ()) {String Item= S.substring (split_index+1, split_index+1+Len);    Ret.add (item); Next_start= split_index+1+Len; Split_index= S.indexof (":", Next_start); Len=integer.valueof (s.substring (Next_start, Split_index));} what' s more, ' while (Next_start < s.length ()) "are great checking for cases!

Solution:

 Public classCodec {//encodes a list of strings to a single string.     PublicString Encode (list<string>STRs) {        if(STRs = =NULL)            Throw NewIllegalArgumentException ("STRs is null"); StringBuffer Buffer=NewStringBuffer ();  for(String str:strs) {buffer.append (Str.length ()); Buffer.append (":");        Buffer.append (str); }        returnbuffer.tostring (); }    //decodes a single string to a list of strings.     PublicList<string>Decode (String s) {List<String> ret =NewArraylist<string> (); intNext_start = 0;  while(Next_start <s.length ()) {            intSplit_index = S.indexof (":", Next_start); intLen =integer.valueof (s.substring (Next_start, Split_index)); String Item= S.substring (split_index+1, split_index+1+Len);            Ret.add (item); Next_start= split_index+1+Len; }        returnret; }}//Your Codec object would be instantiated and called as such://Codec Codec = new Codec ();//Codec.decode (Codec.encode (STRs));

[leetcode#271] Encode and Decode Strings