Create 286-Walls-and-Gates.java

SharmaTushar1 · web-flow · commit 5cf9e5dc8e4a · 2022-07-19T17:09:25.000+05:30
diff --git a/java/286-Walls-and-Gates.java b/java/286-Walls-and-Gates.java
@@ -0,0 +1,37 @@
+//Same as rotting oranges
+//Time complexity will be O(N^2) since we are basically traversing every value in the grid.
+
+class Solution {
+    public void wallsAndGates(int[][] rooms) {
+        Queue<int[]> q = new LinkedList<>();
+        int m = rooms.length; 
+        int n = rooms[0].length;
+        for (int i=0; i<m; i++) {
+            for (int j=0; j<n; j++) {
+                if (rooms[i][j]==0) 
+                    q.add(new int[]{i, j});
+            }
+        }
+        if (q.size()==0)
+            return;
+        int[][] dirs = {{-1,0}, {0,-1}, {1,0}, {0,1}};
+        int dis = 0;
+        while (!q.isEmpty()) {
+            ++dis;
+            int[] cur = q.poll();
+            int row = cur[0];
+            int col = cur[1];
+            for (int[] dir: dirs) {
+                int x = row+dir[0];
+                int y = col+dir[1];
+                if (x>=m || y>=n || x<0 || y<0 || rooms[x][y]!=Integer.MAX_VALUE)
+                    continue;
+                q.add(new int[]{x, y});
+                //since cur is basically the index of door (which is equal to 0)
+                //So, we can just grab that value (rooms[row][col]) and add 1 to it and change it every time
+                rooms[x][y] = rooms[row][col]+1;
+                //So, one level further from door (value 0) is equal to 1. Now, we do bfs from that position so value will be 2 and so on.
+            }
+        }
+    }
+}
