Rotting Oranges

class Solution {
public:
    int orangesRotting(vector<vector<int>>& grid) {
        queue<pair<pair<int,int>,int>> q;
        int n=grid.size();
        int m=grid[0].size();
        int vis[n][m];
        int cfresh=0;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(grid[i][j]==2)
                {
                    q.push({{i,j},0});
                    vis[i][j]=2;
                }
                else
                {
                    vis[i][j]=0;
                }
                if(grid[i][j]==1)
                {
                    cfresh++;
                }
            }
        }
        int dx[4]={-1,0,1,0};
        int dy[4]={0,1,0,-1};
        int c=0;
        int tm=0;
        while(!q.empty())
        {
            int r=q.front().first.first;
            int col=q.front().first.second;
            int t=q.front().second;
            tm = max(t,tm);
            q.pop();
            for(int k=0;k<4;k++)
            {
                int nr=r+dx[k];
                int nc=col+dy[k];

                if((nr>=0 && nr<n) && (nc>=0 && nc<m) && vis[nr][nc]==0 && grid[nr][nc]==1)
                {
                    q.push({{nr,nc},t+1});
                    vis[nr][nc]=2;
                    c++;
                }
            }
        }
        if(c!=cfresh)
        {
            return -1;
        }
        return tm;
    }
};