Add rotting oranges

src/main/java/com/thealgorithms/datastructures/graphs/RottingOranges.java

@@ -0,0 +1,114 @@
+package com.thealgorithms.datastructures.graphs;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * Multi-source Breadth-First Search (BFS) implementation for the Rotting Oranges problem.
+ *
+ * <p>Algorithm explanation:
+ * https://en.wikipedia.org/wiki/Breadth-first_search
+ *
+ * <p>Problem reference:
+ * https://leetcode.com/problems/rotting-oranges/
+ *
+ * <p>Given a grid where:
+ * <ul>
+ *     <li>0 represents an empty cell</li>
+ *     <li>1 represents a fresh orange</li>
+ *     <li>2 represents a rotten orange</li>
+ * </ul>
+ *
+ * <p>Returns the minimum number of minutes required for all fresh oranges
+ * to become rotten. Returns {@code -1} if it is impossible.
+ *
+ * <p>Time Complexity: O(m × n)
+ * <br>Space Complexity: O(m × n)
+ */
+public class RottingOranges {
+
+    private static final int[] DEL_ROW = {-1, 0, 1, 0};
+    private static final int[] DEL_COL = {0, 1, 0, -1};
+
+    private static final class Cell {
+        private final int row;
+        private final int col;
+        private final int minute;
+
+        Cell(int row, int col, int minute) {
+            this.row = row;
+            this.col = col;
+            this.minute = minute;
+        }
+    }
+
+    /**
+     * Executes the Rotting Oranges algorithm.
+     *
+     * @param grid the input grid
+     * @return minimum minutes required to rot all fresh oranges,
+     *         or -1 if impossible
+     */
+    public int run(int[][] grid) {
+
+        if (grid == null || grid.length == 0 || grid[0].length == 0) {
+            return 0;
+        }
+
+        int rows = grid.length;
+        int cols = grid[0].length;
+
+        // Create a copy so original input is not modified
+        int[][] copy = new int[rows][cols];
+
+        for (int i = 0; i < rows; i++) {
+            copy[i] = grid[i].clone();
+        }
+
+        Queue<Cell> queue = new LinkedList<>();
+        int freshOranges = 0;
+
+        // Find all rotten oranges and count fresh oranges
+        for (int row = 0; row < rows; row++) {
+            for (int col = 0; col < cols; col++) {
+
+                if (copy[row][col] == 2) {
+                    queue.offer(new Cell(row, col, 0));
+                } else if (copy[row][col] == 1) {
+                    freshOranges++;
+                }
+            }
+        }
+
+        if (freshOranges == 0) {
+            return 0;
+        }
+
+        int rottedFresh = 0;
+        int minutes = 0;
+
+        // Multi-source BFS
+        while (!queue.isEmpty()) {
+
+            Cell current = queue.poll();
+
+            minutes = Math.max(minutes, current.minute);
+
+            for (int i = 0; i < 4; i++) {
+
+                int newRow = current.row + DEL_ROW[i];
+                int newCol = current.col + DEL_COL[i];
+
+                if (newRow >= 0 && newRow < rows && newCol >= 0 && newCol < cols && copy[newRow][newCol] == 1) {
+
+                    copy[newRow][newCol] = 2;
+                    rottedFresh++;
+
+                    queue.offer(new Cell(newRow, newCol, current.minute + 1));
+                }
+            }
+        }
+
+        return rottedFresh == freshOranges ? minutes : -1;
+    }
+}

src/test/java/com/thealgorithms/datastructures/graphs/RottingOrangesTest.java

@@ -0,0 +1,134 @@
+package com.thealgorithms.datastructures.graphs;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class RottingOrangesTest {
+
+    @Test
+    void testAllOrangesRotInSingleMinute() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1, 1}, {1, 1, 0}, {0, 1, 1}};
+
+        assertEquals(4, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testImpossibleToRotAllOranges() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1, 1}, {0, 1, 1}, {1, 0, 1}};
+
+        assertEquals(-1, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testNoFreshOranges() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 2}, {2, 2}};
+
+        assertEquals(0, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testNoRottenOranges() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{1, 1}, {1, 1}};
+
+        assertEquals(-1, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testEmptyGrid() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {};
+
+        assertEquals(0, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testSingleRottenOrange() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2}};
+
+        assertEquals(0, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testSingleFreshOrange() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{1}};
+
+        assertEquals(-1, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testSingleFreshOrangeNextToRottenOrange() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1}};
+
+        assertEquals(1, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testMultipleRottenSources() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1, 0, 2}, {1, 1, 1, 1}, {0, 1, 1, 1}};
+
+        assertEquals(3, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testFreshOrangeBlockedByEmptyCells() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 0, 1}, {0, 0, 0}, {1, 0, 1}};
+
+        assertEquals(-1, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testLinearSpread() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1, 1, 1, 1}};
+
+        assertEquals(4, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testVerticalSpread() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2}, {1}, {1}, {1}};
+
+        assertEquals(3, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testGridWithOnlyEmptyCells() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{0, 0}, {0, 0}};
+
+        assertEquals(0, rottingOranges.run(grid));
+    }
+
+    @Test
+    void testComplexGrid() {
+        RottingOranges rottingOranges = new RottingOranges();
+
+        int[][] grid = {{2, 1, 1}, {1, 1, 1}, {1, 1, 1}};
+
+        assertEquals(4, rottingOranges.run(grid));
+    }
+}