Merge branch 'master' of github.com:g1patil/algorithms

Author: g1patil

src/main/java/matrix/IslandPerimeter.java

@@ -0,0 +1,69 @@
+package matrix;
+
+import annotation.Platform;
+import annotation.Quality;
+import annotation.Site;
+import annotation.Stage;
+import org.junit.Test;
+
+/**
+ * 463. Island Perimeter
+ */
+@Platform(Site.LEETCODE)
+@Quality(Stage.TESTED)
+public class IslandPerimeter {
+
+    public int islandPerimeter(int[][] grid) {
+        int[] start = getStartingCell(grid);
+        return dfs(grid, new boolean[grid.length][grid[0].length], start[0], start[1]);
+    }
+
+    private int dfs(int[][] grid, boolean[][] visited, int row, int col) {
+        if (!isValid(row, col, grid) || visited[row][col])
+            return 0;
+
+        visited[row][col] = true;
+        return getPerimeter(grid, row, col) + dfs(grid, visited, row + 1, col)
+                + dfs(grid, visited, row - 1, col)
+                + dfs(grid, visited, row, col + 1)
+                + dfs(grid, visited, row, col - 1);
+    }
+
+    private int getPerimeter(int[][] grid, int row, int col) {
+        int[][] dirs = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
+        int perimeter = 0;
+
+        for (int[] dir : dirs) {
+            int newRow = row + dir[0];
+            int newCol = col + dir[1];
+            if (newRow < 0 || newRow >= grid.length || newCol < 0 || newCol >= grid[0].length || grid[newRow][newCol] == 0) {
+                perimeter++;
+            }
+        }
+
+        return perimeter;
+    }
+
+    private boolean isValid(int row, int col, int[][] grid) {
+        return row >= 0 && row < grid.length && col >= 0 && col < grid[0].length && grid[row][col] == 1;
+    }
+
+    /**
+     * Gets the fist cell which is part of the island
+     * @param grid the island grid
+     * */
+    private int[] getStartingCell(final int[][] grid) {
+        for (int i = 0; i < grid.length; i++) {
+            for (int j = 0; j < grid[0].length; j++) {
+                if (grid[i][j] == 1)
+                    return new int[]{i, j};
+            }
+        }
+        return new int[]{-1, -1};
+    }
+
+    @Test
+    public void test() {
+        System.out.println(islandPerimeter(new int[][]{{0, 1, 0}, {0, 1, 1}, {0, 1, 0},}));
+    }
+}