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].

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

Try it on Leetcode

Here, we are going to solve the problem using DFS(Depth First Search) based on HINT 1 given at bottom of the question.

In above Java solution, img is the color of starting pixel to be filled.

1) If it is same as new color [because it is already filled], there is no need to proceed and return the given image.

2)Then do DFS, starting from given sr, sc we change color of new pixel

3) By doing DFS, check all 4 directional neighboring pixels.

 a) If neighboring pixels are valid, then update particular coordinates with new pixel value.

 b) After updating, then check for 4 directional neighboring pixels from that point and repeat above steps (a)

Time Complextity: O(N)

Space Complexity: O(N)

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