general BFS to finnd minimum time

Author: Arjiit

BFS/rottenOranges.java

@@ -0,0 +1,47 @@
+class Cell {
+    int x;
+    int y;
+    public Cell(int x, int y) {
+        this.x = x;
+        this.y = y;
+    }
+}
+class Solution {
+    int[][] dir = {{-1,0}, {1,0}, {0,-1}, {0,1}};
+    public int orangesRotting(int[][] grid) {
+        Queue<Cell> q = new LinkedList<>(); 
+        int count_fresh = 0;
+        for (int i=0; i<grid.length; i++) {
+            for (int j=0; j<grid[0].length; j++) {
+                if (grid[i][j] == 2) {
+                    Cell rottenCell = new Cell(i, j);
+                    q.add(rottenCell);
+                } else if (grid[i][j] == 1) {
+                    count_fresh++;
+                }
+            }
+        }
+        
+        if (count_fresh == 0) return 0;
+        int time = 0;
+        while(!q.isEmpty()) {
+        time++;
+        int size = q.size();
+        for (int times = 0; times < size; times++) {
+           Cell curCell = q.poll();
+            for (int[] d: dir) {
+                int new_r = d[0] + curCell.x;
+                int new_c = d[1] + curCell.y;
+                if (new_r >=0 && new_c >= 0 && new_r < grid.length && new_c < grid[0].length && (grid[new_r][new_c] == 1)) {
+                    Cell newCell = new Cell(new_r, new_c);
+                    grid[new_r][new_c] = 2;
+                    q.add(newCell);
+                    count_fresh--;
+                }
+            }
+        }
+        }
+        if (count_fresh != 0) return -1;
+        return time == 0 ? -1: time-1;
+    }
+}