CODEWITHSUNDEEP
javaarraysmultidimensional-arraycompression
Nathan
Nathan

Reputation: 1347

A bit of array manipulation

I have a 2d array String compressedColors[][], which is filled with numbers between 0 and n(Where n is the number of colors in an image). Now I'm trying to compress my array even more for writing to a file, and one idea I had is replacing consecutive identical elements with some sort of multiplication operator. As in I'd like:

compressedColors[0][0]=="1"

compressedColors[0][1] == "1" to become

compressedColors[0][0]=="2*1"

compressedColors[0][1] == ""

This would need to happen for large numbers of consecutive idenitcal elements, and I only want the compression to go across the second dimension of the array. If two rows are filled with 0's, I want 2 seperate n*0 values at compressedColors[x][0].

I know this is asking a lot, but any ideas how I could accomplish this? I don't even know where to start... Thanks!

Upvotes: 0

Views: 58

Answers (2)

martin jakubik
martin jakubik

Reputation: 4148

To answer your question you need to implement both compression and de-compression.

The algorithm for compression (thanks @harold for the term "run-length encoding"), would be something like:

  // for an uncompressed image of height h and width w, stored in int colors[][]

  for row = 0 to height
    for column = 0 to width

      // gets the value
      value = colors[row][column]

      // calculates how long the value repeats
      runLength = 0
      nextValue = value
      i = 0
      while(nextValue == value)
        i++
        runLength++
        nextValue = colors[row][column + i]

      // sets the runlength and the value
      compressedColors[row][column] = runLength
      compressedColors[row][column + 1] = value

      // moves to next different value
      column = column + runLength

Then, to decompress, you need to interpret every odd column as a run-length and every even column as a value.

Upvotes: 1

touko
touko

Reputation: 2047

I wrote an example which should at least give you an idea how to achieve a solution to your problem. I didn't have a chance to test this out right now so I'm not sure if this will work without modifications.

public static String[][] compress(String[][] sArray){
    for(String s[] : sArray){
        int current = 0;
        while(current <= s.length){
            int sequentials = 1;
            while(s[current].equals(s[current+sequentials])){
                s[current+sequentials] = "";
                sequentials++;
                if(current+sequentials>s.length) 
                    break;
            }
            if(sequentials > 1) s[current] = sequentials+"*"+s[current];
            current++;
        }
    }   
    return sArray;
}

Upvotes: 1

Related Questions