solves #130 in java

Author: anishLearnsToCode

Diff for: README.md

@@ -117,7 +117,7 @@
 | 125  | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome)                                                                                        |                                   [![Java](assets/java.png)](src/ValidPalindrome.java) [![Python](assets/python.png)](python/valid_palindrome.py)                                    |                                                                                                                                   |
 | 128  | [Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence)                                                                |                                                           [![Java](assets/java.png)](src/LongestConsecutiveSequence.java)                                                            |                                                                                                                                   |
 | 129  | [Sum Root to Leaf Numbers](https://leetcode.com/problems/sum-root-to-leaf-numbers)                                                                        |                                                              [![Java](assets/java.png)](src/SumRootToLeafNumbers.java)                                                               |                                                                                                                                   |
-| 130  | [Surrounded Regions](https://leetcode.com/problems/surrounded-regions)                                                                                    |                                                                                                                                                                                      |                                                                                                                                   |
+| 130  | [Surrounded Regions](https://leetcode.com/problems/surrounded-regions)                                                                                    |                                                                [![Java](assets/java.png)](src/SurroundedRegions.java)                                                                |                                                                                                                                   |
 | 131  | [Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning)                                                                          |                                                                                                                                                                                      |                                                                                                                                   |
 | 133  | [Clone Graph](https://leetcode.com/problems/clone-graph)                                                                                                  |                                                                                                                                                                                      |                                                                                                                                   |
 | 134  | [Gas Station](https://leetcode.com/problems/gas-station)                                                                                                  |                                                                                                                                                                                      |                                                                                                                                   |

Diff for: src/SurroundedRegions.java

@@ -0,0 +1,92 @@
+// https://leetcode.com/problems/surrounded-regions
+// T: O(m * n)
+// S: O(m * n)
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class SurroundedRegions {
+    private record Position(int row, int column) {
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            Position position = (Position) o;
+            if (row != position.row) return false;
+            return column == position.column;
+        }
+
+        @Override
+        public int hashCode() {
+            return 31 * row + column;
+        }
+
+        public Position top() {
+            return new Position(row - 1, column);
+        }
+
+        public Position right() {
+            return new Position(row, column + 1);
+        }
+
+        public Position bottom() {
+            return new Position(row + 1, column);
+        }
+
+        public Position left() {
+            return new Position(row, column - 1);
+        }
+    }
+
+    public void solve(char[][] board) {
+        final Set<Position> visited = new HashSet<>();
+        final Set<Position> current = new HashSet<>();
+        final int rows = board.length, columns = board[0].length;
+
+        for (int row = 1 ; row < rows - 1 ; row++) {
+            for (int column = 1 ; column < columns - 1 ; column++) {
+                if (board[row][column] == 'O') {
+                    final boolean isBorderRegion = markRegion(board, new Position(row, column), visited, current);
+                    if (!isBorderRegion) {
+                        captureRegion(board, current);
+                    }
+                    current.clear();
+                }
+            }
+        }
+    }
+
+    private boolean markRegion(char[][] board, Position position, Set<Position> visited, Set<Position> region) {
+        if (isInvalidPosition(board, position) || visited.contains(position) || isX(board, position)) return false;
+        visited.add(position);
+        region.add(position);
+        boolean top = markRegion(board, position.top(), visited, region);
+        boolean right = markRegion(board, position.right(), visited, region);
+        boolean bottom = markRegion(board, position.bottom(), visited, region);
+        boolean left = markRegion(board, position.left(), visited, region);
+        return top || right || bottom || left || isBorderPosition(board, position);
+    }
+
+    private boolean isX(char[][] board, Position position) {
+        return board[position.row][position.column] == 'X';
+    }
+
+    private boolean isBorderPosition(char[][] board, Position position) {
+        return position.row == 0
+                || position.row == board.length - 1
+                || position.column == 0
+                || position.column == board[0].length - 1;
+    }
+
+    private boolean isInvalidPosition(char[][] board, Position position) {
+        return position.row < 0
+                || position.row >= board.length
+                || position.column < 0
+                || position.column >= board[0].length;
+    }
+
+    private void captureRegion(char[][] board, Set<Position> positions) {
+        for (Position position : positions) {
+            board[position.row][position.column] = 'X';
+        }
+    }
+}