Spiral array from a random starting position - c++

Question

Consider an array
0000
0000
0000
Then a number generated in a complete random position in the array
0000
0000
00x0
What I want to do is knowing the position of the number, make it go through the array in a spiral order. I can't find something in c++, it's the only language I know.
I already know how to go in spiral order from element [0][0] to [1][2] (clockwise), but how do I do it if my initial position is random? Then, how do I go backwards, anti-clockwise? And so on, but the start should be from that random position(2 numbers generated random will be the positions).

Answer 1

This code only works if you point is in the center of your array. If you add correct bounds checking this should work as you describe. I made the assumption(based on your first example) that when you finish all existing elements you move to the outer set. ie
0000
0000
00x0
becomes
2222
2111
21x1
touching them in this order
6 7 8 9
11 1 2 3
10 5 X 4
with 2 represent the second circle and 1 the first circle.
the output from this program is (i just stored the"radius" in each element)
pre traversal
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
post traversal
2 2 2 2 2
2 1 1 1 2
2 1 0 1 2
2 1 1 1 2
2 2 2 2 2
// what is the maximum possible radius
int getMaxRadius(int x, int y, int size)
{
int toReturn = std::abs(size-x);
if(std::abs(size-y) > toReturn)
toReturn = std::abs(size -y);
return toReturn ;
}
//is the curernt element next to the current center
bool nextTo(int xCenter, int yCenter, int x, int y, int radius )
{
//if it
if(std::abs(xCenter - x) > radius || std::abs(yCenter - y) > radius)
{
return false;
}
return true;
}
void circular(int** array, int xCenter, int yCenter, int size)
{
int curRadius = 1;
int maxRadius = getMaxRadius(xCenter, yCenter,size);
while( curRadius<maxRadius)
{
//start to the top left of the cur radius
int curX = xCenter - curRadius;
int curY = yCenter - curRadius;
//go right
while(nextTo(xCenter, yCenter, curX, curY, curRadius ))
{
array[curX][curY] = curRadius;
curX ++;
}
curX--;//we went one too far
//go down
while(nextTo(xCenter, yCenter, curX, curY, curRadius ))
{
array[curX][curY] = curRadius;
curY ++;
}
curY--;//we went one too far
//go left
while(nextTo(xCenter, yCenter, curX, curY, curRadius ))
{
array[curX][curY] = curRadius;
curX --;
}
curX++;//we went one too far
//goUP
while(nextTo(xCenter, yCenter, curX, curY, curRadius ))
{
array[curX][curY] = curRadius;
curY --;
}
curY++;//we went one too far
curRadius ++;
}
}