Feature iterative flood fill

src/main/java/com/thealgorithms/others/IterativeFloodFill.java

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+package com.thealgorithms.others;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * Implementation of the Flood Fill algorithm using an iterative BFS (Breadth-First Search) approach.
+ *
+ * <p>The Flood Fill algorithm is used to fill connected areas in an image with a new color, starting from a specified point.
+ * This implementation uses an iterative BFS approach with a queue
+ * instead of recursion to avoid stack overflow issues with large images.</p>
+ *
+ * <p><b>Implementation Features:</b></p>
+ * <ul>
+ *   <li>Supports 8-connected filling (horizontal, vertical, and diagonal directions)</li>
+ *   <li>Uses BFS traversal through {@link java.util.Queue}</li>
+ *   <li>Includes nested {@code Point} class to represent pixel coordinates</li>
+ *   <li>Iterative approach avoids stack overflow for large images</li>
+ * </ul>
+ *
+ * <p><b>Time Complexity:</b> O(M × N) where M and N are the dimensions of the image</p>
+ * <p><b>Space Complexity:</b> O(M × N) in the worst case the queue stores every pixel</p>
+ *
+ * @see <a href="https://www.geeksforgeeks.org/dsa/flood-fill-algorithm">Flood Fill Algorithm - GeeksforGeeks</a>
+ * @see <a href="https://en.wikipedia.org/wiki/Flood_fill">Flood Fill Algorithm - Wikipedia</a>
+ */
+public final class IterativeFloodFill {
+    private IterativeFloodFill() {
+    }
+
+    /**
+     * Iteratively fill the 2D image with new color
+     *
+     * @param image    The image to be filled
+     * @param x        The x co-ordinate at which color is to be filled
+     * @param y        The y co-ordinate at which color is to be filled
+     * @param newColor The new color which to be filled in the image
+     * @param oldColor The old color which is to be replaced in the image
+     * @see <a href=https://www.geeksforgeeks.org/dsa/flood-fill-algorithm>FloodFill BFS<a/>
+     */
+    public static void floodFill(final int[][] image, final int x, final int y, final int newColor, final int oldColor) {
+        if (image.length == 0 || image[0].length == 0 || newColor == oldColor || shouldSkipPixel(image, x, y, oldColor)) {
+            return;
+        }
+
+        Queue<Point> queue = new LinkedList<>();
+        queue.add(new Point(x, y));
+
+        int[] dx = {0, 0, -1, 1, 1, -1, 1, -1};
+        int[] dy = {-1, 1, 0, 0, -1, 1, 1, -1};
+
+        while (!queue.isEmpty()) {
+            Point currPoint = queue.poll();
+
+            if (shouldSkipPixel(image, currPoint.x, currPoint.y, oldColor)) {
+                continue;
+            }
+
+            image[currPoint.x][currPoint.y] = newColor;
+
+            for (int i = 0; i < 8; i++) {
+                int curX = currPoint.x + dx[i];
+                int curY = currPoint.y + dy[i];
+
+                if (!shouldSkipPixel(image, curX, curY, oldColor)) {
+                    queue.add(new Point(curX, curY));
+                }
+            }
+        }
+    }
+
+    /**
+     * Represents a point in 2D space with integer coordinates.
+     */
+    private static class Point {
+        final int x;
+        final int y;
+
+        Point(final int x, final int y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+
+    /**
+     * Checks if a pixel should be skipped during flood fill operation.
+     *
+     * @param image    The image to get boundaries
+     * @param x        The x co-ordinate of pixel to check
+     * @param y        The y co-ordinate of pixel to check
+     * @param oldColor The old color which is to be replaced in the image
+     * @return {@code true} if pixel should be skipped, else {@code false}
+     */
+    private static boolean shouldSkipPixel(final int[][] image, final int x, final int y, final int oldColor) {
+
+        if (x < 0 || x >= image.length || y < 0 || y >= image[0].length || image[x][y] != oldColor) {
+            return true;
+        }
+
+        return false;
+    }
+}

src/test/java/com/thealgorithms/others/IterativeFloodFillTest.java

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+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+class IterativeFloodFillTest {
+
+    @Test
+    void testForEmptyImage() {
+        int[][] image = {};
+        int[][] expected = {};
+
+        IterativeFloodFill.floodFill(image, 4, 5, 3, 2);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForSingleElementImage() {
+        int[][] image = {{1}};
+        int[][] expected = {{3}};
+
+        IterativeFloodFill.floodFill(image, 0, 0, 3, 1);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForEmptyRow() {
+        int[][] image = {{}};
+        int[][] expected = {{}};
+
+        IterativeFloodFill.floodFill(image, 4, 5, 3, 2);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForImageOne() {
+        int[][] image = {
+            {0, 0, 0, 0, 0, 0, 0},
+            {0, 3, 3, 3, 3, 0, 0},
+            {0, 3, 1, 1, 5, 0, 0},
+            {0, 3, 1, 1, 5, 5, 3},
+            {0, 3, 5, 5, 1, 1, 3},
+            {0, 0, 0, 5, 1, 1, 3},
+            {0, 0, 0, 3, 3, 3, 3},
+        };
+
+        int[][] expected = {
+            {0, 0, 0, 0, 0, 0, 0},
+            {0, 3, 3, 3, 3, 0, 0},
+            {0, 3, 2, 2, 5, 0, 0},
+            {0, 3, 2, 2, 5, 5, 3},
+            {0, 3, 5, 5, 2, 2, 3},
+            {0, 0, 0, 5, 2, 2, 3},
+            {0, 0, 0, 3, 3, 3, 3},
+        };
+
+        IterativeFloodFill.floodFill(image, 2, 2, 2, 1);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForImageTwo() {
+        int[][] image = {
+            {0, 0, 1, 1, 0, 0, 0},
+            {1, 1, 3, 3, 3, 0, 0},
+            {1, 3, 1, 1, 5, 0, 0},
+            {0, 3, 1, 1, 5, 5, 3},
+            {0, 3, 5, 5, 1, 1, 3},
+            {0, 0, 0, 5, 1, 1, 3},
+            {0, 0, 0, 1, 3, 1, 3},
+        };
+
+        int[][] expected = {
+            {0, 0, 2, 2, 0, 0, 0},
+            {2, 2, 3, 3, 3, 0, 0},
+            {2, 3, 2, 2, 5, 0, 0},
+            {0, 3, 2, 2, 5, 5, 3},
+            {0, 3, 5, 5, 2, 2, 3},
+            {0, 0, 0, 5, 2, 2, 3},
+            {0, 0, 0, 2, 3, 2, 3},
+        };
+
+        IterativeFloodFill.floodFill(image, 2, 2, 2, 1);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForImageThree() {
+        int[][] image = {
+            {1, 1, 2, 3, 1, 1, 1},
+            {1, 0, 0, 1, 0, 0, 1},
+            {1, 1, 1, 0, 3, 1, 2},
+        };
+
+        int[][] expected = {
+            {4, 4, 2, 3, 4, 4, 4},
+            {4, 0, 0, 4, 0, 0, 4},
+            {4, 4, 4, 0, 3, 4, 2},
+        };
+
+        IterativeFloodFill.floodFill(image, 0, 1, 4, 1);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForSameNewAndOldColor() {
+        int[][] image = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        int[][] expected = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        IterativeFloodFill.floodFill(image, 0, 1, 1, 1);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForBigImage() {
+        int[][] image = new int[100][100];
+
+        assertDoesNotThrow(() -> IterativeFloodFill.floodFill(image, 0, 0, 1, 0));
+    }
+
+    @Test
+    void testForBelowZeroX() {
+        int[][] image = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        int[][] expected = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        IterativeFloodFill.floodFill(image, -1, 1, 1, 0);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForBelowZeroY() {
+        int[][] image = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        int[][] expected = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        IterativeFloodFill.floodFill(image, 1, -1, 1, 0);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForAboveBoundaryX() {
+        int[][] image = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        int[][] expected = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        IterativeFloodFill.floodFill(image, 100, 1, 1, 0);
+        assertArrayEquals(expected, image);
+    }
+
+    @Test
+    void testForAboveBoundaryY() {
+        int[][] image = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        int[][] expected = {{1, 1, 2}, {1, 0, 0}, {1, 1, 1}};
+
+        IterativeFloodFill.floodFill(image, 1, 100, 1, 0);
+        assertArrayEquals(expected, image);
+    }
+}