CODEWITHSUNDEEP
javastringcomparison
Yosi199
Yosi199

Reputation: 1804

Implement my own string comparison

I've been given this question of string comparison. I had to write a method to compare two strings without using java's built in string comparison methods. Also it suppose to be around 3 - 5 lines of code long. The method should return 0 for equal, 1 for string 'a' is bigger then string 'b', -1 for string 'a' is smaller then 'b'

Now, I know Java compares string based on the int value of each char so I tried to do this thing, which works but is definitely not 3-5 lines of code long:

public int compare(String s1, String s2){

    int result = 0;
    int count = 0; // The counter for the first string integer values sum
    int count2 = 0; // The counter for the second string integer values sum

    for(int c=0; c<s1.length(); c++){
        count = count +s1.charAt(c);
    }

    for (int c2=0; c2<s2.length(); c2++){
        count2 = count2 +s2.charAt(c2);
    }

    //***** some condition statement to check which is bigger and then return the result

Upvotes: 0

Views: 2600

Answers (5)

Eypros
Eypros

Reputation: 5723

Considering 2 String a and b a solution might be:

int comp = 0;
for(int i = 0; i < Math.min(a.length(), b.length()); i++) 
    if((comp = a.charAt(i) - b.charAt(i)) != 0)
        return comp;
return a.length() < b.length() ? -1 : a.length() == b.length() ? 0 : 1;

which calculates the difference of every char in the same position upto the smaller String length and if they are all 0 returns the smaller String.

Edit: I don't know the reason for the downvoting might be but anyway on a quick test it works as expected (and it's 5 lines long).

Upvotes: 0

learningProgramming
learningProgramming

Reputation: 13

Here is my try. I tested it a bit and it seems to work. If it doesn't, then sorry. I've got much to learn.

So, my try is based on how Strings are treated in Java, i.e. they are immutable. Any String you create goes into a "Constant String Pool". When you make a new reference to a String that is already in the pool, the JVM makes that reference indicate to the String object that already exists in the pool. So I think it is clear that 2 identical String references are pointing to the exact same String object, even if they have been created separately. Based on this, my method returns 0 if the references are equal and does something else otherwise. Please excuse the return at the end, I know it's ugly, the program won't compile without. I also know(hope) it is unreachable. Here is the function(6 lines): 

public int compare(String s1, String s2) {

    if (s1 == s2) return 0;
    else {
        for (int i = 0; i < Math.min(s1.length(), s2.length()); i++) {
            if (s1.charAt(i) > s2.charAt(i)) return 1;
            else return -1;
        }
    }
    return -2;
}

Upvotes: 0

blgt
blgt

Reputation: 8205

Have you considered doing a simple lexicographic comparison rather than comparing lengths (or whatever it is that you try to do, it's not particularly easy to tell):

for(int i=0; i<a.length() && i<b.length(); i++) {
    if(a.charAt(i) != b.charAt(i))
        return a.charAt(i) < b.charAt(i) ? -1 : 1;
}
return a.length() < b.length() ? -1 : a.length() == b.length() ? 0 : 1;

This is basically the same as what java.lang.Strings do except it only uses public methods.

Upvotes: 5

luiscosta
luiscosta

Reputation: 855

I think this recursive approach might work for you:

public static int compare(String a, String b, int pos){
    if(a.charAt(pos) == b.charAt(pos) && pos >= a.length() && pos >= b.length())
        return 0;
    else if(a.charAt(pos) > b.charAt(pos))
        return 1;
    else if(a.charAt(pos) < b.charAt(pos))
        return -1;
    else {
        pos++;
        if(pos < a.length() && pos < b.length())
            return compare(a,b,pos);
        else if(pos < a.length() && pos >= b.length())
            return 1;
        else if(pos >= a.length() && pos < b.length())
            return -1;
        else return 0;
    }
}

You have to call the compare method on main with the variable pos at 0 like this: 

public static void main(String[] args) {

    String a = "azzz";
    String b = "azz";

    System.out.println("" + compare(a,b,0));
}

Hope this helps.

Upvotes: 0

dev
dev

Reputation: 1507

This should work... (haven't compiled so not 100% sure). I know it isn't < 5 lines but it should work correctly. Can try to shorten it after that.

for(int i=0; i < s1.length(); i++)
{
    if(s2.length()-1 < i)
      return -1;
    if(s1.charAt(i) > s2.charAt(i))
      return -1;
    if(s1.charAt(i) < s2.charAt(i))
      return 1;
}
if(s2.length() > s1.length())
  return 1;
return 0;

Upvotes: -2

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