从数组数组中读取任意长度的数组

我很努力地编写一个从阵列中读取数组而不创建临时数组的算法。从数组数组中读取任意长度的数组

这里是我的想法：

[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.

一个例子（POS = 12，长度= 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) 
[ ][ ][ ][ ][ ][ ][ ][ ] 
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]

感谢您的帮助！

来源

2016-08-22 Romain

*“看来它不工作” *你能解释更多的是什么？发生什么事？ – 4castle

我的意思是，当我运行该方法时，我不输出正确的序列。但我一直在想，我认为我搞砸了srcOffset＆position 由于指针不移动，位置指针会给出错误的值。 – Romain

我在这里结束，用了实施：

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; 
}

来源

2016-08-22 13:54:53 Romain

从数组数组中读取任意长度的数组

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