733. Flood Fill

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本文介绍了一种在二维图像中实现“洪水填充”的算法，通过递归深度优先搜索(DFS)和广度优先搜索(BFS)两种方法改变指定起始点及其相连相同颜色像素的颜色。

题目描述：

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.

思路一：递归 DFS

class Solution {
    public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
        if (image[sr][sc] == newColor)
            return image;
        fill(image, sr, sc, image[sr][sc], newColor);
        return image;
    }
    public void fill(int[][] image, int sr, int sc, int color, int newColor)
    {
        if (sr < 0 || sr >= image.length || sc < 0 || sc >= image[0].length || image[sr][sc] != color)
            return;
        image[sr][sc] = newColor;
        fill(image, sr - 1, sc, color, newColor);
        fill(image, sr + 1, sc, color, newColor);
        fill(image, sr, sc - 1, color, newColor);
        fill(image, sr, sc + 1, color, newColor);
    }
}

思路二：BFS

class Solution {
    public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
        int[][] increments = new int[][]{{0, +1}, {0, -1}, {-1, 0}, {+1, 0}};
        boolean[][] visited = new boolean[image.length][image[0].length];
        int color = image[sr][sc];
        Queue<int[]> queue = new LinkedList<>();
        queue.add(new int[]{sr, sc});
        while (!queue.isEmpty())
        {
            int[] tmp = queue.poll();
            visited[tmp[0]][tmp[1]] = true;
            for (int[] increment : increments)
            {
                int nr = tmp[0] + increment[0];
                int nc = tmp[1] + increment[1];
                if (nr >= 0 && nr < image.length && nc >= 0 && nc < image[0].length && !visited[nr][nc] && image[nr][nc] == color)
                    queue.add(new int[] {nr, nc});
            }
            image[tmp[0]][tmp[1]] = newColor;
        }
        return image;
    }
}