Resize a 2D map - arrays

Question

I'm developing a 2D map editor for a game and I need a way to increase or decrease the size of the grid/map uniformly in all directions.
Suppose you have a 3x3 map with a sort of "cross" symbol.
(arrays are zero-indexed. They start with 0)
Like this:
0,1,0
1,1,1
0,1,0
The array would look like this:
map = [0,1,0,1,1,1,0,1,0]
So, tile index 4 would be the center of the map.
I'd like to increase the size from 3x3 to 5x5 for example. So I end up with this:
0,0,0,0,0
0,0,1,0,0
0,1,1,1,0
0,0,1,0,0
0,0,0,0,0
The new map array should end up like this:
map = [0,0,0,0,0,0,0,1,0,0,0,1,1,1,0,0,0,1,0,0,0,0,0,0]
What's a good way of doing this?

Answer 1

Here are two functions for increase and decrease. The parameter arr is your one-dimensional map and xWidth is the width (and of course the height) of your grid.
I had a question with a similar background here on Stackoverflow so many thanks to willywonka_dailyblah who helped me on the j and i indices.
public int[] increase_grid(int[] arr, int xWidth)
{
int newWidth = (xWidth+2);
int[] result = new int[newWidth * newWidth];
int count=0;
while(count<newWidth)
{
result[count++] = 0;
}
for (int i=0;i<xWidth;i++)
{
result[count++] = 0;
for (int j=0;j<xWidth;j++)
{
result[count++] = arr[i * xWidth + j];
}
result[count++] = 0;
}
while(count<(newWidth*newWidth))
{
result[count++] = 0;
}
return result;
}
public int[] decrease_grid(int[] arr, int xWidth)
{
int newWidth = (xWidth-2);
int[] result = new int[newWidth*newWidth];
for(int i=0; i< newWidth;i++)
{
for (int j=0;j< newWidth;j++)
{
result[i* newWidth + j] = arr[(i+1) * xWidth + (j+1)];
}
}
return result;
}
And I have this print function:
public void print_arr(int[] a, int xWidth)
{
for(int i=0;i<xWidth;i++)
{
for(int j=0;j<xWidth;j++)
{
System.out.print(a[i * xWidth + j]+" ");
}
System.out.println();
}
System.out.println();
}
You call these functions like:
int[] map = new int[]{0,1,0,1,1,1,0,1,0};
print_arr(map, 3);
map = increase_grid(map, 3);
print_arr(map, 5);
map = increase_grid(map, 5);
print_arr(map, 7);
map = decrease_grid(map, 7);
print_arr(map, 5);
So you have to pass the current size of your map and either call increase or decrease. Beware, that the these functions include a nested for-loop. Thus, they are less scale-able on greater grid sizes. I think there may be a solution to wrap even this into a loop-sequence, which runs without nesting.