733. Flood Fill

https://leetcode.com/problems/flood-fill/

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].

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Note - check for newColor == origColor corner case to avoid infinite loop
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Related problems

island-perimeter
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BFS - Non recursive - Queue based 

Time - O(r * c)
Space - O(r * c)

	class Solution {
	public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
	int oldColor = image[sr][sc];
	// Corner case, no op, starting cell
	if (oldColor == newColor) {
	return image;
	}
	Queue<int[]> q = new LinkedList<int[]>();
	image[sr][sc] = newColor;
	q.offer(new int[] {sr, sc});
	int[][] dirs = new int[][] {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
	while (!q.isEmpty()) {
	int[] current = q.poll();
	for (int[] d: dirs) {
	int nr = current[0] + d[0];
	int nc = current[1] + d[1];
	if (isValid(image, nr, nc, oldColor)) {
	image[nr][nc] = newColor;
	q.offer(new int[] {nr, nc});
	}
	}
	}
	return image;
	}
	private boolean isValid(int[][] image, int nr, int nc, int oldColor) {
	return nr >= 0 && nc >= 0 && nr < image.length && nc < image[0].length && image[nr][nc] == oldColor;
	}
	}

view raw 733.FloodFillBFS.java hosted with ❤ by GitHub

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DFS - recursive - faster than BFS

Time - O(r * c)

	class Solution {
	int[][] dirs = new int[][] {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
	public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
	int oldColor = image[sr][sc];
	// Corner case, no op, starting cell
	if (oldColor == newColor) {
	return image;
	}
	image[sr][sc] = newColor;
	dfs(image, sr, sc, oldColor, newColor);
	return image;
	}
	private void dfs(int[][] image, int r, int c, int oldColor, int newColor) {
	for (int[] d: dirs) {
	int nr = r + d[0];
	int nc = c + d[1];
	if (isValid(image, nr, nc, oldColor)) {
	image[nr][nc] = newColor;
	dfs(image, nr, nc, oldColor, newColor);
	}
	}
	}
	private boolean isValid(int[][] image, int nr, int nc, int oldColor) {
	return nr >= 0 && nc >= 0 && nr < image.length && nc < image[0].length && image[nr][nc] == oldColor;
	}
	}

view raw 733.FloodFillDFS.java hosted with ❤ by GitHub