PaintFill function

Implement the “paint fill” function that one might see on many image editing programs. That is, given a screen (represented by a 2-dimensional array of Colors), a point, and a new color, fill in the surrounding area until you hit a border of that color.


First, let’s visualize how this method works. When we call Paint Fill (eg, “click” paint fill in the image editing application) on, say, a green pixel, we want to “bleed” outwards. Pixel by pixel, we expand outwards calling PaintFill on the surrounding pixel. When we hit a pixel that is not green, we stop. Surrounding green pixels may still be painted if they are touched by another Paint Fill operation.
We can implement this algorithm recursively:

enum Color {
 Black, White, Red, Yellow, Green
 }
 boolean PaintFill(Color[][] screen, int x, int y, Color ocolor,
 Color ncolor) {
 if (x < 0 || x >= screen[0].length ||
 y < 0 || y >= screen.length) {
 return false;
 }
 if (screen[y][x] == ocolor) {
 screen[y][x] = ncolor;
 PaintFill(screen, x - 1, y, ocolor, ncolor); // left
 PaintFill(screen, x + 1, y, ocolor, ncolor); // right
 PaintFill(screen, x, y - 1, ocolor, ncolor); // top
 PaintFill(screen, x, y + 1, ocolor, ncolor); // bottom
 }
 return true;
 }

 boolean PaintFill(Color[][] screen, int x, int y, Color ncolor) {
 return PaintFill(screen, x, y, screen[y][x], ncolor);
 }