Floodfill (BFS)

///Antonelli Alen

#include <iostream>
#include <vector>
#include <queue>
#define INF (1<<29)
using namespace std;

int dx[] = {0, 0, 1,-1};
int dy[] = {1,-1, 0, 0};

struct grafo {
    vector<string> ady;
    vector< vector<int> > dist;
    vector< pair<int,int> > ini;
    queue< pair<int,int> > cola;
    int n, m, p;

    void leer()
    {
        cin>>n>>m;

        ady.resize(n);
        dist = vector< vector<int> > (n+1, vector<int> (m, INF) );

        for(int i=0; i<n; i++)
            cin>>ady[i];
    }

    bool visitable (int x, int y)
    {
        if ((0<=x && x<n) && (0<=y && y<m) )
            if( ady[x][y]!='#' )
                return true;
        return false;
    }

    void BFS ()
    {
        for(int i=0; i<n; i++) /// laterales
        {
            if ( visitable(i, 0) )
                ini.push_back( {i,0} );
            if ( visitable(i, m-1) )
                ini.push_back( {i,m-1} );
        }

        for(int i=0; i<m; i++) /// superior inferior
        {
            if ( visitable(0, i) )
                ini.push_back( {0,i} );
            if ( visitable(n-1,i) )
                ini.push_back( {n-1,i} );
        }

        for(int i=0; i<ini.size(); i++)
        {
            int x = ini[i].first;
            int y = ini[i].second;

            dist[x][y] = 0;
            cola.push( ini[i] );
        }

        while(cola.size())
        {
            int x = cola.front().first;
            int y = cola.front().second;
            cola.pop();

            for(int i=0; i<4; i++)
            {
                int vx = x+dx[i];
                int vy = y+dy[i];

                if ( visitable(vx,vy) )
                    if ( dist[x][y]+1 < dist[vx][vy] )
                    {
                        dist[vx][vy] = dist[x][y]+1;
                        cola.push( {vx,vy} );
                    }
            }
        }

        for(int i=0; i<n; i++)
        {
            for(int j=0; j<m; j++)
            {
                if (ady[i][j]=='#')
                    cout<<"#  ";
                else if (dist[i][j]==INF)
                    cout<<"N  ";
                else if (dist[i][j]>9)
                    cout<<dist[i][j]<<" ";
                else
                   cout<<dist[i][j]<<"  ";
            }
            cout<<endl;
        }

        cin>>p;
        int x, y;
        for(int i=0; i<p; i++)
        {
            cin>>x>>y;
            cout<<x<<" "<<y<<" -> ";
            if(dist[x-1][y-1]==INF)
                cout<<"NO"<<endl;
            else cout<<dist[x-1][y-1]<<endl;
        }
    }
};

int main()
{
    grafo g;
    g.leer();
    g.BFS();

    return 0;
}

/*

6 10
##########
____###__#
____#_##_#
##__####_#
#________#
##########

4
1 1
5 2
4 9
3 6

*/