Create 994.cpp

Author: JanaSabuj

994/994.cpp

@@ -0,0 +1,50 @@
+class Solution {
+public:
+    int dx[4] = {0, 0, 1, -1};
+    int dy[4] = {1, -1, 0, 0};
+    bool valid(int r, int c, int n, int m) {return (r >= 0 and r < n and c >= 0 and c < m);}
+    
+    int orangesRotting(vector<vector<int>>& grid) {
+        queue<pair<int,int>> q;
+        int n = grid.size();
+        int m = grid[0].size();
+        
+        int fresh = 0;
+        for(int i = 0; i < n; i++){
+            for(int j = 0; j < m; j++){
+                if(grid[i][j] == 2){
+                    q.push({i,j});// rotten will start spreading
+                }else if(grid[i][j] == 1)
+                    fresh++;
+            }
+        }
+        
+        if(fresh == 0)
+            return 0;
+        
+        int time = -1;
+        while(!q.empty()){
+            int sz = q.size();
+            time++;
+            
+            while(sz--){
+                auto [x,y] = q.front();
+                q.pop();
+                
+                for(int i = 0; i < 4; i++){
+                    int r = x + dx[i];
+                    int c = y + dy[i];
+                    
+                    if(valid(r,c,n,m) and grid[r][c] == 1){
+                        // only go to a fresh apple
+                        q.push({r,c});
+                        grid[r][c] = 2;   
+                        fresh--;
+                    }
+                }
+            }
+        }
+        
+        return fresh == 0 ? time: -1;
+    }
+};