Number of Islands

Author: nikoo28

src/main/java/leetcode/medium/NumberOfIslands.java

@@ -0,0 +1,38 @@
+package leetcode.medium;
+
+public class NumberOfIslands {
+
+  int numIslands(char[][] grid) {
+    if (grid == null || grid.length == 0 || grid[0].length == 0) {
+      return 0;
+    }
+
+    int count = 0;
+
+    for (int i = 0; i < grid.length; i++)
+      for (int j = 0; j < grid[0].length; j++)
+        if (grid[i][j] == '1') {
+          dfs(grid, i, j);
+          count++;
+        }
+
+    return count;
+  }
+
+  private void dfs(char[][] grid, int i, int j) {
+    if (i < 0 || i >= grid.length
+        || j < 0 || j >= grid[0].length
+        || grid[i][j] == '0') {
+      return;
+    }
+
+    grid[i][j] = '0'; // Mark the cell as visited
+
+    // Explore all four directions
+    dfs(grid, i + 1, j);
+    dfs(grid, i - 1, j);
+    dfs(grid, i, j + 1);
+    dfs(grid, i, j - 1);
+  }
+
+}

src/test/java/leetcode/medium/NumberOfIslandsTest.java

@@ -0,0 +1,64 @@
+package leetcode.medium;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class NumberOfIslandsTest {
+
+  private final NumberOfIslands numberOfIslands;
+
+  NumberOfIslandsTest() {
+    numberOfIslands = new NumberOfIslands();
+  }
+
+  @Test
+  void testNumIslands1() {
+    char[][] grid = {
+        {'1', '1', '0', '0', '0'},
+        {'1', '1', '0', '0', '0'},
+        {'0', '0', '1', '0', '0'},
+        {'0', '0', '0', '1', '1'}
+    };
+    assertEquals(3, numberOfIslands.numIslands(grid));
+  }
+
+  @Test
+  void testNumIslands2() {
+    char[][] grid = {
+        {'1', '1', '1', '1', '0'},
+        {'1', '1', '0', '1', '0'},
+        {'1', '1', '0', '0', '0'},
+        {'0', '0', '0', '0', '0'}
+    };
+    assertEquals(1, numberOfIslands.numIslands(grid));
+  }
+
+  @Test
+  void testNumIslands3() {
+    char[][] grid = {
+        {'1'}
+    };
+    assertEquals(1, numberOfIslands.numIslands(grid));
+  }
+
+  @Test
+  void testNumIslands4() {
+    char[][] grid = {
+        {'0', '0', '0'},
+        {'0', '0', '0'},
+        {'0', '0', '0'}
+    };
+    assertEquals(0, numberOfIslands.numIslands(grid));
+  }
+
+  @Test
+  void testNumIslands5() {
+    char[][] grid = {
+        {'1', '0', '1', '0'},
+        {'0', '1', '0', '1'},
+        {'1', '0', '1', '0'}
+    };
+    assertEquals(6, numberOfIslands.numIslands(grid));
+  }
+}