key = "D";
for (y = 1; y <= Bottom; y++) {
  count = 0;
  for (x = 1; x <= Right; x++) {
    if ([x,y] == key) {
      count++;
    }
  }
  for (x = Right; count > 0; x--) {
    if ([x,y] == key) {
      [x+count,y] = "Z";
      count--;
    }
    [x+count,y] = [x,y];
  }  
}