Array von beliebiger Länge aus einem Array von Arrays lesen

Question

Ich habe Schwierigkeiten, einen Algorithmus zu schreiben, der ein Array aus einem Array von Arrays an Ort und Stelle liest, ohne ein temporäres Array zu erstellen.

Hier ist meine Idee:

[data correspond to a byte[][] that contains the data we want to read from] 
[each arrays can be of arbitrary sizes. No assumption can be done there] 
[limit is the sum of bytes that has been wrote to data beforehand. (Appending an array of size X increment limit by X - 1)] 
[position is the current position that has been read by previous calls to read(...)] 

1) Skip until array that belongs to position is reached 
2) Copy from saved position in the array to the output array 
3) Move to next array 
4) Copy as much bytes as we can into the output buffer 
5) Repeat 3-4 until output buffer is filled with the proper amount of data or we've reached the end of the data. 

Ein Beispiel (pos = 12, Länge = 16):

[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ] // Skip this row as pos > row.length 
[ ][ ][X][X][X][X][X]   // Read from position 2 (row.length - relative pos) until end of array 
[X][X][X][X][X][X][X][X]  // Read entire array as length left > row.length 
[X][X][X][ ][ ][ ][ ][ ][ ] // Read from 0 to length left (aka 3) 
[ ][ ][ ][ ][ ][ ][ ][ ] 
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ] 

Vielen Dank für jede Hilfe!

Answer 1

Hier ist die Implementierung I ended-up mit:

public int read(byte[] into, int dstOffset, int length) { 
    if (!isComplete()) { 
     throw new IllegalStateException("Data is not complete yet"); 
    } 

    int pointer = 0; 
    int byteRead = 0; 
    int total = 0; 

    if (VERBOSE) 
     Dog.d("Array size : " + data.length + " ID : " + id); 
    for (int i = 0; i < data.length && (length > 0 || position >= limit); i++) { 
     if (position > (pointer + data[i].length)) { 
      pointer += data[i].length; 
      if (VERBOSE) 
       Dog.d("Skip -> I = " + i + ", Data length = " + data[i].length + ", Position = " + position + ", Pointer = " + pointer + ", Limit = " + limit); 
     } else { 
      if (VERBOSE) 
       Dog.d("I = " + i + ", Data length = " + data[i].length + ", Position = " + position + ", Pointer = " + pointer + ", Limit = " + limit); 
      // We are in the right array 
      int srcOffset = position - pointer; // This is the starting position in our target array 
      int relativeLimit = Math.min(limit - pointer, data[i].length); // The is the ending position in our target array 

      byteRead = Math.min(relativeLimit - srcOffset, length); // Now the number is the byte read is either the number between start and end or the requested length 

      if (VERBOSE) 
       Dog.d("I = " + i + ", srcOffset = " + srcOffset + ", dstOffset = " + dstOffset + ", byteRead = " + byteRead + " out of " + data[i].length + " (limit is = " + limit + ", pointer = " + pointer + ")"); 
      System.arraycopy(data[i], srcOffset, into, dstOffset, byteRead); 

      length -= byteRead; // We've read X bytes, so we still have to read (length - X) 
      dstOffset += byteRead; // We need to start next write at previous position + X 
      total += byteRead; // Counter to keep track of byte we've read 

      pointer += data[i].length; // Current read position 
      position += byteRead; // Current position 
      if (VERBOSE) 
       Dog.d("Left to write = " + length + ", byteRead = " + byteRead + ", total = " + total); 
     } 
    } 

    if (VERBOSE) 
     Dog.d("Wrote a total of :" + total); 
    return total; 
}