solves maze

Author: anishLearnsToCode

Diff for: README.md

@@ -337,6 +337,7 @@
 | 500  | [Keyboard Row](https://leetcode.com/problems/keyboard-row)                                                                                                             |                                                             [![Java](assets/java.png)](src/KeyBoardRow.java) [![Python](assets/python.png)](python/keyboard_row.py)                                                              |                                                                                                                                   |
 | 501  | [Find Mode in Binary Search Tree](https://leetcode.com/problems/find-mode-in-binary-search-tree)                                                                       |                                            [![Java](assets/java.png)](src/FindModeInBinarySearchTree.java) [![Python](assets/python.png)](python/find_mode_in_binary_search_tree.py)                                             |                                                                                                                                   |
 | 504  | [Base 7](https://leetcode.com/problems/base-7)                                                                                                                         |                                                                   [![Java](assets/java.png)](src/Base7.java) [![Python](assets/python.png)](python/base_7.py)                                                                    |                                                                                                                                   |
+| 505  | [The Maze II](https://leetcode.com/problems/the-maze-ii)                                                                                                               |                                                                                          [![Java](assets/java.png)](src/TheMazeII.java)                                                                                          |                                                                                                                                   |
 | 506  | [Relative Ranks](https://leetcode.com/problems/relative-ranks)                                                                                                         |                                                           [![Java](assets/java.png)](src/RelativeRanks.java) [![Python](assets/python.png)](python/relative_ranks.py)                                                            |                                                                                                                                   |
 | 507  | [Perfect Number](https://leetcode.com/problems/perfect-number)                                                                                                         |                                                      [![Java](assets/java.png)](src/CheckPerfectNumber.java) [![Python](assets/python.png)](python/check_perfect_number.py)                                                      |                                                                                                                                   |
 | 509  | [Fibonacci Number](https://leetcode.com/problems/fibonacci-number)                                                                                                     |                                                         [![Java](assets/java.png)](src/FibonacciNumber.java) [![Python](assets/python.png)](python/fibonacci_number.py)                                                          |                                                                                                                                   |

Diff for: src/TheMazeII.java

@@ -0,0 +1,78 @@
+// https://leetcode.com/problems/the-maze-ii
+// T: O(m * n * log(m * n))
+// S: O(m * n)
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.PriorityQueue;
+import java.util.Queue;
+
+public class TheMazeII {
+    private static final int[][] DIRECTIONS = new int[][] {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+
+    public int shortestDistance(int[][] maze, int[] start, int[] destination) {
+        final int rows = maze.length, columns = maze[0].length;
+        final int[][] distance = dijkstra(maze, start);
+        return distance[destination[0]][destination[1]] == Integer.MAX_VALUE ? -1 : distance[destination[0]][destination[1]];
+    }
+
+    // T: O(m * n * log(mn))
+    // S: O(m * n)
+    public int[][] dijkstra(int[][] maze, int[] start) {
+        final int[][] distance = getDistances(maze.length, maze[0].length);
+        final Queue<int[]> queue = new PriorityQueue<>(Comparator.comparingInt(a -> a[2]));
+
+        queue.add(new int[] { start[0], start[1], 0 });
+
+        while (!queue.isEmpty()) {
+            final int[] s = queue.poll();
+            final int row = s[0], column = s[1], d = s[2];
+
+            if (distance[row][column] <= d) {
+                continue;
+            }
+
+            distance[row][column] = d;
+
+            for (int[] position: validPositions(maze, s[0], s[1])) {
+                final int newDistance = distance[row][column] + manhattanDistance(s[0], s[1], position);
+                queue.add(new int[] { position[0], position[1], newDistance});
+            }
+        }
+
+        return distance;
+    }
+
+    // T: O(m + n)
+    // S: O(1)
+    private static List<int[]> validPositions(int[][] grid, int row, int column) {
+        final List<int[]> result = new ArrayList<>();
+        for (int[] direction : DIRECTIONS) {
+            int i = row, j = column;
+            while (i >= 0 && j >= 0 && i < grid.length && j < grid[0].length && grid[i][j] == 0) {
+                i += direction[0];
+                j += direction[1];
+            }
+            result.add(new int[] { i - direction[0], j - direction[1] });
+        }
+        return result;
+    }
+
+    // T: O(m * n)
+    // S: O(m * n)
+    private static int[][] getDistances(int rows, int columns) {
+        final int[][] result = new int[rows][columns];
+        for (int i = 0 ; i < rows ; i++) {
+            for (int j = 0 ; j < columns ; j++) {
+                result[i][j] = Integer.MAX_VALUE;
+            }
+        }
+        return result;
+    }
+
+    // T: O(1), S: O(1)
+    private static int manhattanDistance(int row, int column, int[] position) {
+        return Math.abs(row - position[0]) + Math.abs(column - position[1]);
+    }
+}