将两个字符串编码/解码为一个字符串，然后返回两个

Question

This is an interview question. I was thinking of a solution in java. This questions seems very simple, is there a catch here?

I was thinking of the following solution:

string1 + 1*hash(String1) + string2 + 2*hash(String2).

If I concat strings like this, then I can decode them as well easily into 2 separate strings.

Am I missing something in the question?

Answer 1

Encode:

String encoded = new JsonArray().add(str1).add(str2).toString();

Decode:

JsonArray arr = JsonArray.readFrom(encoded);
String str1 = arr.get(0).asString();
String str2 = arr.get(1).asString();

Here I use minimal-json lib, but it's pretty similar with any other JSON library as well.

Note that it's usually a bad idea to invent new formats of encoding the information into the string as you have plenty of existing ones (xml, json, yaml, etc.) which already solved all the possible issues like symbol escaping and exception handling.

Answer 2

To encode:

String encoded = ""+str1.length()+"/"+str1+str2;

To decode:

String[] temp = encoded.split("/", 2);
int length1 = Integer.parseInt(temp[0]);
String str1 = temp[1].substring(0, length1);
String str2 = temp[1].substring(length1);

Explanation:
The encoded string is in the form "<number>/<str1><str2>" . When you call split(regex, limit) the size of the resulting array will be at most limit , considering only the first matches of regex . Thus even if your strings contain the character / you can be sure that the resulting array will be {"<number>", "<str1><str2>"} .
the substring(begin, end) return a string starting at begin inclusive and ending at end exclusive , giving you a resulting substring of end-begin length. Since you are calling it with values (0, str1.length()) what you get is exactly str1 . The last call will return a substring from str1.length() , which is also the index of the first character of str2 , to the end of the string (which is the end of str2 ).
Reference: String javadoc page

Answer 3

One way is to use the length of the first string.

// encode
String concat = string1 + string2;

// decode
String str1 = concat.substring( 0, string1.length() );
String str2 = concat.substring( string1.length(), concat.length() );

Another way is to use a delimiter. But the delimiter character should not be included in any of the strings to be joined.

// encode
String concat = "hello" + "`" + "world!";

// decode
String[] decoded = concat.split("`");
String str1 = decoded[0];
String str2 = decoded[1];