C++ - Zadatak Poplava :: BFS obilazak matrice

/*
    Zadatak: Poplava

    Izracunati povrsinu ogradjenog dijela matrice oko tocke zadane koordinatama
    (drugim i trecim brojem kod unosa)

    KLASICNI BFS SA BROJANJEM POLJA

    Autor: Kristijan Burnik, Udruga informatičara Božo Težak

    GMail: kristijanburnik

*/
#include <iostream>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <queue>


using namespace std;

typedef pair <int, int> pos;
#define X first
#define Y second
#define mp make_pair
int N,M;

bool canmove( pos a ) {
    return (a.X >=0 && a.X < N) && (a.Y >=0 && a.Y < M) && (mat[a.X][a.Y] != '#');
}

// uzorak kretanja
pos DELTA[4] = {mp(-1,0),mp(1,0),mp(0,-1),mp(0,1)};
vector < pos > delta(DELTA,DELTA+4);
const int DS = delta.size();

// matrice za obilazak
vector < vector <char> > mat;
vector < vector <bool> > seen;


int floodfill(pos current) {
    queue <pos> q;
    q.push(current);
    seen[current.X][current.Y] = true;
    int count = 0;
    while (!q.empty()) {
        current = q.front(); q.pop();
        count++;
        for (int i = 0 ; i < DS; i++) {
            pos next = mp(current.X+delta[i].X,current.Y+delta[i].Y);
            if (canmove(next) && !seen[next.X][next.Y]) {
                q.push(next);
                seen[next.X][next.Y] = true;
            }
        }
    }

    return count;
}

int main(void) {

    pos current;
    cin >> N >> M >> current.X >> current.Y;
    current.X--; current.Y--;

    mat.resize(N); seen.resize(N);
    for (int i = 0; i < N; i++) {
        mat[i].resize(M);
        seen[i].resize(M);
        for(int j = 0; j < M; j++) cin >> mat[i][j];
   }
   cout << floodfill(current) << endl;

   return 0;
}

// Primjeri //
/*

8 8 1 1
........
#.#.#.#.
########
.#....#.
.#..#.#.
....#...
########
........

8 8 4 1
........
#.#.#.#.
########
.#....#.
.#..#.#.
....#...
########
........

8 8 8 3
........
#.#.#.#.
########
.#....#.
.#..#.#.
....#...
########
........


*/