Flood Fill (Easy Uber)

update May 15,2018 20:33

LeetCode

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].

Basic Idea:

典型的在矩阵图中DFS的题目，需要注意在 helper function 中传入 oldColor 参数来记录原本需要被染色的颜色。

• C++ Code:

    class Solution {
        int dr[4] = {-1, 0, 1, 0};
        int dc[4] = {0, 1, 0, -1};
  
        void dfs(vector<vector<int>>& image, int sr, int sc, int oldColor, int newColor) {
            if (sr < 0 || sr >= image.size() || sc < 0 || sc >=image[0].size()) return;
            if (image[sr][sc] == oldColor) {
                image[sr][sc] = newColor;
                for (int i = 0; i < 4; ++i) {
                    int r = sr + dr[i];
                    int c = sc + dc[i];
                    dfs(image, r, c, oldColor, newColor);
                }
            }
        }
    public:
        vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int newColor) {
            if (newColor == image[sr][sc]) return image;
            dfs(image, sr, sc, image[sr][sc], newColor);
            return image;
        }
    };