FloodFill.go

/*
An image is represented by a 2-D array of integers, each integer representing the pixel value of the image (from 0 to 65535).
Given a coordinate (sr, sc) representing the starting pixel (row and column) of the flood fill, and a pixel value newColor, "flood fill" the image.
To perform a "flood fill", consider the starting pixel, plus any pixels connected 4-directionally to the starting pixel of the same color as the starting pixel, plus any pixels connected 4-directionally to those pixels (also with the same color as the starting pixel), and so on. Replace the color of all of the aforementioned pixels with the newColor.
At the end, return the modified image.

Example 1:
Input:
image = [[1,1,1],[1,1,0],[1,0,1]]
sr = 1, sc = 1, newColor = 2
Output: [[2,2,2],[2,2,0],[2,0,1]]
Explanation:
From the center of the image (with position (sr, sc) = (1, 1)), all pixels connected
by a path of the same color as the starting pixel are colored with the new color.
Note the bottom corner is not colored 2, because it is not 4-directionally connected
to the starting pixel.

Note:
The length of image and image[0] will be in the range [1, 50].
The given starting pixel will satisfy 0 <= sr < image.length and 0 <= sc < image[0].length.
The value of each color in image[i][j] and newColor will be an integer in [0, 65535].

*/

package main

import (
	"log"
)

func main() {
	log.Println("main(): Floodfilling..")
	log.Println(floodFill([][]int{[]int{1,1,1},[]int{1,1,0},[]int{1,0,1}}, 1, 1, 2))
	// floodFill([][]int{[]int{1,1,1},[]int{1,1,0},[]int{1,0,1}}, 1, 1, 2)
}

func floodFill(image [][]int, sr int, sc int, newColor int) [][]int {

	// check which pixels are on north/south/east/west to the designated start
	// floodfill ones with the same color as the starter
	// make note of the floodfilled pixels and enlist their
	// N/E/S/W neighbors to continue floodfilling

	// make note of starting pixel color
	var starterColor int
	if len(image) > sr && len(image[sr]) > sc {
		starterColor = image[sr][sc]
		// log.Println(starterColor)
	} else {
		log.Fatal("Invalid starting pixel")
	}

	pixelsToFill := [][]int{{sr, sc}}

	run := 0
	for len(pixelsToFill) > 0 {
		// for each pixel in pixelsToFill,
		// - check it's color, and fill if it's starterColor
		// - if filled, remove it from pixelsToFill and add its north/south/east/west neighbors to pixelsToFill

		// coordinates of the point to fill (last element in pixelsToFill)
		log.Println(pixelsToFill)
		log.Printf("Run: %d\n\n", run)
		run++
		// return image

		ssr := pixelsToFill[len(pixelsToFill)-1][0]
		ssc := pixelsToFill[len(pixelsToFill)-1][1]

		// TODO: ensure that {ssr,ssc} is filled
		if ssr >= 0 && ssr < len(image) && ssc >= 0 && ssc < len(image[ssr]) {	// ensure valid coordinates
			if image[ssr][ssc] != newColor {
				image[ssr][ssc] = newColor
			}
		}

		// remove {ssr,ssc} from list of pixels to fill
		pixelsToFill = pixelsToFill[:len(pixelsToFill)-1]


		// add neighbors to the list of pixels to fill
		if ssr-1 >= 0 && ssr-1 < len(image) && ssc >= 0 && ssc < len(image[ssr-1]) {	// north
			if image[ssr-1][ssc] == starterColor {
				pixelsToFill = append(pixelsToFill, []int{ssr-1,ssc})
			}
		}

		if ssr+1 >= 0 && ssr+1 < len(image) && ssc >= 0 && ssc < len(image[ssr+1]) {	// south
			if image[ssr+1][ssc] == starterColor {
				pixelsToFill = append(pixelsToFill, []int{ssr+1,ssc})
			}
		}

		if ssr >= 0 && ssr < len(image) && ssc-1 >= 0 && ssc-1 < len(image[ssr]) {	// east
			if image[ssr][ssc-1] == starterColor {
				pixelsToFill = append(pixelsToFill, []int{ssr,ssc-1})
			}
		}

		if ssr >= 0 && ssr < len(image) && ssc+1 >= 0 && ssc+1 < len(image[ssr]) {	// west
			if image[ssr][ssc+1] == starterColor {
				pixelsToFill = append(pixelsToFill, []int{ssr,ssc+1})
			}
		}

		/* // north of {ssr,ssc}
		if (ssr - 1) >= 0 { // valid row?
			north := image[ssr-1][ssc]
			if north == starterColor {
				// fill
				image[ssr-1][ssc] = newColor

				// remove
				pixelsToFill = pixelsToFill[:len(pixelsToFill)-1]

				// add neighbors
				if ssr-2 >= 0 && image[ssr-2][ssc] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-2][ssc]}) // north
				}

				if (ssc+1) < len(image[ssr-1]) && image[ssr-1][ssc+1] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-1][ssc+1]}) // east
				}

				// south was already filled

				if (ssc-1) >= 0 && image[ssr-1][ssc-1] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-1][ssc-1]}) // west
				}

			}
		}

		// south
		if (ssr + 1) < len(image) { // valid row?
			south := image[ssr+1][ssc]
			if south == starterColor {
				// fill
				image[ssr+1][ssc] = newColor

				// remove
				pixelsToFill = pixelsToFill[:len(pixelsToFill)-1]

				// add neighbors
				if ssr+2 < len(image) && image[ssr-2][ssc] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-2][ssc]}) // north
				}

				if (ssc+1) < len(image[ssr-1]) && image[ssr-1][ssc+1] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-1][ssc+1]}) // east
				}

				// south was already filled

				if (ssc-1) >= 0 && image[ssr-1][ssc-1] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr-1][ssc-1]}) // west
				}

			}
		}

		// east
		if (ssc + 1) < len(image[ssr]) {
			east := image[ssr][ssc+1]

			if east == starterColor {
				// fill
				image[ssr][ssc+1] = newColor

				// remove from to-be-filled list
				pixelsToFill = pixelsToFill[:len(pixelsToFill)-1]

				// add eligible neighbors to to-be-filled list
				if (ssr+1) < len(image) && image[ssr+1][ssc+1] == starterColor {
					pixelsToFill = append(pixelsToFill, []int{image[ssr+1][ssc+1]})	// nort
				}

				// east

				// south

				// west
			}
		} */

	}

	return image

}