Problem: 179 Flood fill algorithm

README.md

@@ -6,7 +6,7 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 178 |
+| Total Problems | 179 |
 
 </center>
 
@@ -203,6 +203,7 @@ Include contains single header implementation of data structures and some algori
 | Print Minimum Spanning Tree( MST ) of a given graph using Kruskal's algorithm.| [kruskalMST.cpp](graph_problems/kruskalMST.cpp)|
 | Create a program to generate a Huffman encoding for each character as a table.|[huffman_encoding.cpp](greedy_problems/huffman_encoding.cpp)|
 | Search a given word in a 2D board containing letters. The word can be constructed by sequentially traversing adjacent horizontal or vertical cells. In a sequence to form word, letter on same position can not be used more than once. (Check top of file for examples.)|[grid_word_search.cpp](graph_problems/grid_word_search.cpp)|
+| Given a 2D screen, location of the pixel and new value of the color to fill, replace the color of the pixel and all the adjacent(up, below, left, right) same colored pixel with new color. This is same as flood fill (remember the bucket symbol) a region in MS-PAINT.| [flood_fill.cpp](graph_problems/flood_fill.cpp)|
 
 ### Greedy Problems
 | Problem | Solution |

graph_problems/flood_fill.cpp

@@ -0,0 +1,83 @@
+/*
+ * Given a 2D screen, location of the pixel and new value of the color to fill, replace the color of the
+ * pixel and all the adjacent(up, below, left, right) same colored pixel with new color.
+ * 
+ * This is same as flood fill (remember the bucket symbol) a region in MS-PAINT.
+ * 
+ * [[1 1 1 2 2 1 1]
+ *  [1 1 1 2 1 1 1]
+ *  [1 2 2 2 1 3 3]
+ *  [4 4 1 2 7 9 9]]
+ * 
+ * The screen is 0-indexed.
+ * Start at pixel (1, 3) and replace color 2 with color 5, in this pixel and all the adjacent same
+ * color pixels.
+ * 
+ * Therefore, the answer would be:
+ * [[1 1 1 5 5 1 1]
+ *  [1 1 1 5 1 1 1]
+ *  [1 5 5 5 1 3 3]
+ *  [4 4 1 5 7 9 9]]
+ * 
+ * Approach: Use the simple depth first search to search adjacent pixels of same color
+ * and mark them with new color. 
+ */
+
+#include <iostream>
+#include <vector>
+
+bool is_valid(int grid_height, int grid_width, int sr, int sc) {
+    return (sr >= 0 && sr < grid_height && sc >= 0 &&
+        sc < grid_width); 
+}
+
+void flood_fill_helper(std::vector<std::vector<int>>& image, int sr, int sc, int new_color, int old_color)
+{
+    if (!is_valid(image.size(), image[0].size(), sr, sc)) {
+        return;
+    }
+
+    if (image[sr][sc] != old_color) {
+        return;
+    }
+
+    image[sr][sc] = new_color;
+    flood_fill_helper(image, sr - 1, sc, new_color, old_color);
+    flood_fill_helper(image, sr + 1, sc, new_color, old_color);
+    flood_fill_helper(image, sr, sc - 1, new_color, old_color);
+    flood_fill_helper(image, sr, sc + 1, new_color, old_color);
+}
+
+std::vector<std::vector<int>> flood_fill(std::vector<std::vector<int>>& image, int sr, int sc, int new_color)
+{
+    if (image[sr][sc] != new_color) {
+        int old_color = image[sr][sc];
+        flood_fill_helper(image, sr, sc, new_color, old_color);
+    }
+    return image;
+}
+
+void print_image(const std::vector<std::vector<int>>& image) {
+    for (auto row : image) {
+        for (auto pixel : row) {
+            std::cout << pixel << " ";
+        }
+        std::cout << std::endl;
+    }
+}
+
+int main()
+{
+    std::vector<std::vector<int>> image = {
+        {1, 1, 1, 2, 2, 1, 1},
+        {1, 1, 1, 2, 1, 1, 1},
+        {1, 2, 2, 2, 1, 3, 3},
+        {4, 4, 1, 2, 7, 9, 9}
+    };
+    std::cout << "Current Image:" << std::endl;
+    print_image(image);
+    std::cout << "Applying flood fill at pixel (1,3) to change color to 5:" << std::endl;
+    image = flood_fill(image, 1, 3, 5);
+    print_image(image);
+    return 0;
+}