Merge pull request #43 from ayush1300/patch-1

Create RottingOranges.cpp

Author: shruti170901

RottingOranges.cpp

@@ -0,0 +1,61 @@
+class Solution {
+public:
+    
+    int orangesRotting(vector<vector<int>>& grid) {
+        int i,j;
+        int cnt1=0;
+        queue<pair<int,int> > q;   
+        
+        // The concept of the problem lies in the fact:
+        // Start a bfs with all the rotten oranges in the queue
+        // Traverse in all possible diretions in the grid, and keep track of the levels which also acts as the time to for all the oranges to rott.
+        
+        for(i=0;i<grid.size();i++)
+        {
+            for(j=0;j<grid[i].size();j++)
+            {
+                if(grid[i][j]==2)
+                {
+                    q.push({i,j});
+                }
+                if(grid[i][j]==1)
+                {
+                    cnt1++;
+                }
+            }
+        }
+        
+        
+        int lev=0;
+        int dx[] = {1,0,-1,0};     
+        int dy[] = {0,1,0,-1};
+        while(!q.empty())
+        {
+            int s = q.size();
+            int x;
+            for(x=0;x<s;x++)
+            {
+                auto p = q.front();
+                q.pop();
+                int y;
+                for(y=0;y<4;y++)
+                {
+                    int n_x = p.first + dx[y];
+                    int n_y = p.second + dy[y];
+                    if(n_x>=0 && n_x<grid.size() && n_y>=0 && n_y<grid[0].size() && (grid[n_x][n_y]==1 ))
+                    {
+                        grid[n_x][n_y] = 2;
+                        q.push({n_x,n_y});
+                        cnt1--;
+                    }
+                }
+            }
+            lev++;
+        }
+        if(lev==0 && cnt1==0)
+            return 0;
+        int ans = (cnt1==0) ? lev-1: -1;   
+        return ans;
+        
+    }
+};