应用重力：2D数组

Question

My program consists of a grid composed by a 2D array. The user input deletes certain elements of the grid, leaving blank spaces. My issue is making the elements above the blank spaces drop down.

Originaly I had an array to check if a space is blank, and if is was blank, the element above would be deleted and recreated where there used to be a blank.

My problem is, the array I used to do this was Left->Right, Top->Down (i++, j++), this leaves me with the problem of having to repeat the whole code to get newly built blank spaces. (For example, if I delete something from the 3rd row, the 2nd row would be blank, but I'd have checked the 2nd row already.

Since it would be very uneffective (including overstack errors) I decided to do the reserve, bottom->top, right->left array (i--,j--), my issue with this is that I'm getting an array out of bounds error, even though I made sure its not possible for it to go out of bounds.

Here is the piece of code which is giving problems

public static void dropBall(){
 for (i =Settings.row-1;i>=0;i--){
  for (j =Settings.col-1;i>=0 ; j--){
   if (i <0||j<0)break;
   if (Settings.grid[i+1][j]==666){ 
    //checking if the space below has the 666 ID (666 ID equals to blank)                   
    Settings.grid[i+1][j]=Settings.grid[i][j]; //Deleting the current blank                 
   }
  }
 }
}

Note: Settings.row and Settings.col are similar to something.lenght , meaning they have the lenght of the grid, even though the grid starts at 0.

How can I avoid the outofBounds error in this situation?

Answer 1

• On line3:

    for (j =Settings.col-1;i>=0 ; j--){ 

change to:

                for (j =Settings.col-1;j>=0 ; j--){

• and you can remove the if line after.

• and start your i on Settings.row-2 instead

• try this:

    public static void dropBall(){ for (i =Settings.row-1;i>=0;i--){ for (j =Settings.col-1;j>=0 ; j--){ if (Settings.grid[i+1][j]==666){ //checking if the space below has the 666 ID (666 ID equals to blank) Settings.grid[i+1][j]=Settings.grid[i][j]; //Deleting the current blank Settings.grid[i][j] = 666; } } } } 

Answer 2

1. Start from the second row at the bottom, and not from the first (since there is no row below it):

     for (i = Settings.row-2 ... // instead of row-1 

2. Remove this line (it is redundant):

     if (i <0||j<0)break;