How should I implement the Grassfire Algorithm in C++ - c++

Question

So in my program, I generate a random grid using 2D Arrays where all indexes are initialized to 0. Now, a certain percentage of random indexes are filled with -1 which means that they are impassable/ act like a wall. The user also inputs a certain target index say (i,j) from where he starts and his goal is to reach index (0,0) by taking the shortest path possible.
To find the shortest path, I have to check for the neighbours of each cell, starting from the target location. If they have neighbours, I increment the neighbour value by 1. Refer to my figure for more details. I got the code on how to calculate the shortest path, but I'm stuck with this incrementation part. I tried writing a code but it doesn't seem to work. Any help would be appreciated:-
GRID is generated in the following way:
1 is the user input location, and the goal is to reach X i.e 0,0
-X 0 0 0 0 0 0 0 0 -1
-0 0 0 -1 -1 0 0 0 0 0
-0 0 0 0 -1 0 0 0 0 0
-0 0 0 0 0 0 0 0 0 -1
-0 0 0 0 0 0 0 1 0 0
Starting by incrementing
-X 0 0 0 0 0 0 0 0 -1
-0 0 0 -1 -1 0 0 0 0 0
-0 0 0 0 -1 3 3 3 3 3
-0 0 0 0 0 3 2 2 2 -1
-0 0 0 0 0 3 2 1 2 3
I have only showed it till 3, but it keeps on going until index 0,0 is reached.
void waveAlgorithm(int *array, int height, int width, int x, int y)
{
while (array != NULL)
{
// Assume that index 0 0 is never 1
if (currX == 0 && currY == 0){
break;
}
// Check South
int currX = x;
int currY = y + 1;
if (currX < width && currX > 0 && currY < height && currY >= 0)
{
if (*(array + currX * width + currY) == 0)
{
(*(array + currX * width + currY))++;
}
}
// Check North
currX = x;
currY = y - 1;
if (currX < width && currX > 0 && currY < height && currY >= 0)
{
if (*(array + currX * width + currY) != -1)
{
(*(array + currX * width + currY))++;
}
}
// Check West
currX = x - 1;
currY = y;
if (currX < width && currX > 0 && currY < height && currY >= 0)
{
if (*(array + currX * width + currY) != -1)
{
(*(array + currX * width + currY))++;
}
}
// Check East
currX = x + 1;
currY = y;
if (currX < width && currX > 0 && currY < height && currY >= 0)
{
if (*(array + currX * width + currY) != -1)
{
(*(array + currX * width + currY))++;
}
}
}
}
I am kinda stuck while implementing this program, especially for the the directions that are combinational i.e North East, South East, etc. I tried writing a recursive program but couldn't figure out how to increment the cells
waveAlgorithm(int *arr)
{
if(index is 0,0)
return;
waveAlgorithm(int[i+1][j]);
waveAlgorithm(int[i][j+1]);
waveAlgorithm(int[i-1][j]);
waveAlgorithm(int[i][j-1]);
}