USACO-T036: Overfencing

/*
ID: mickyta1
TASK: maze1
LANG: C++
*/

#include <bits/stdc++.h>
using namespace std;

#define f first
#define s second
typedef pair<int, int> pii;
typedef pair<pii, int> ppi;

const pii dir[4] = {pii(0, 1), pii(0, -1), pii(1, 0), pii(-1, 0)};
const int R = 200 + 5;
const int C = 76 + 5;

int row, col;
char board[R][C];
bool visited[R][C];

bool isInBoard(const pii &x){
    return 2 <= x.f && x.f <= row && 2 <= x.s && x.s <= col;
}

int main(){
    freopen("maze1.in", "r", stdin);
    freopen("maze1.out", "w", stdout);

    scanf("%d%d%*c", &col, &row);
    row *= 2;
    col *= 2;
    for(int i = 1; i <= row + 1; ++i){
        for(int j = 1; j <= col + 1; ++j){
            scanf("%c", &board[i][j]);
        }
        scanf("%*c");
    }
    queue<ppi> que;
    for(int i = 2; i <= row; i += 2){
        visited[i][0] = true;
        que.emplace(pii(i, 0), 0);
        visited[i][col + 2] = true;
        que.emplace(pii(i, col + 2), 0);
    }
    for(int j = 2; j <= col; j += 2){
        visited[0][j] = true;
        que.emplace(pii(0, j), 0);
        visited[row + 2][j] = true;
        que.emplace(pii(row + 2, j), 0);
    }
    int mx = 0;
    while(!que.empty()){
        pii u = que.front().f;
        int dt = que.front().s;
        que.pop();
        mx = max(mx, dt);
        for(int d = 0; d < 4; ++d){
            pii obs = pii(u.f + dir[d].f, u.s + dir[d].s);
            pii v = pii(u.f + 2 * dir[d].f, u.s + 2 * dir[d].s);
            if(isInBoard(v) && board[obs.f][obs.s] == ' ' && !visited[v.f][v.s]){
                visited[v.f][v.s] = true;
                que.emplace(v, dt + 1);
            }
        }
    }
    cout << mx << '\n';

    fclose(stdin);
    fclose(stdout);
    return 0;
}