Add 286_Walls_and_Gates.java

Author: seanprashad

Tree Breadth First Search/286_Walls_and_Gates.java

@@ -0,0 +1,46 @@
+class Solution {
+    public void wallsAndGates(int[][] rooms) {
+        Set<int[]> gates = new HashSet<>();
+
+        for (int row = 0; row < rooms.length; row++) {
+            for (int col = 0; col < rooms[row].length; col++) {
+                if (rooms[row][col] == 0) {
+                    gates.add(new int[] { row, col });
+                }
+            }
+        }
+
+        Queue<int[]> q = new LinkedList<>();
+
+        for (int[] gate : gates) {
+            q.offer(gate);
+        }
+
+        int distance = 0;
+        boolean[][] visited = new boolean[rooms.length][rooms[0].length];
+
+        while (!q.isEmpty()) {
+            int size = q.size();
+
+            for (int i = 0; i < size; i++) {
+                int[] coord = q.poll();
+                int x = coord[0], y = coord[1];
+
+                if (x < 0 || y < 0 || x >= rooms.length || y >= rooms[0].length ||
+                        rooms[x][y] == -1 || visited[x][y]) {
+                    continue;
+                }
+
+                rooms[x][y] = Math.min(rooms[x][y], distance);
+                visited[x][y] = true;
+
+                q.offer(new int[] { x + 1, y });
+                q.offer(new int[] { x - 1, y });
+                q.offer(new int[] { x, y + 1 });
+                q.offer(new int[] { x, y - 1 });
+            }
+
+            ++distance;
+        }
+    }
+}