Problem p03436 (C++)

Buggy submission (status: Time Limit Exceeded):
/*
ll used[10];
ll maxi;

ll dfs(Graph& graph, ll v, ll deep) {
        used[v] = 1;
        vector<ll> maxd;
        maxd.push_back(deep);
        for (int i = 0; i < graph[v].size(); i++) {
                if (used[graph[v][i].to] == 0) {
                        maxd.push_back(dfs(graph, graph[v][i].to, deep + 1));
                }
        }
        sort(all(maxd), greater<ll>());
        if (maxd.size() > 2) {
                chmax(maxi, maxd[0] - deep + maxd[1] - deep);
        }
        else {
                chmax(maxi, maxd[0] - deep);
        }
        return maxd[0];
}
*///dfs
/*
REP(i, n) {
        REP(j, n) {
                dp[i][j] = INF;
        }
}
REP(i, m) {
        ll a, b, c;
        cin >> a >> b >> c;
        dp[a][b] = c;
        dp[b][a] = c;
}
REP(i, n) {
        REP(j, n) {
                REP(k, n) {
                        chmin(dp[j][k], dp[j][i] + dp[i][k]);
                }
        }
}
*///warshall floyd

#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
#define MOD 1000000007
#define REP(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define FOR(i, c)                                                              \
  for (decltype((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ll long long
#define ull unsigned long long
#define all(hoge) (hoge).begin(), (hoge).end()
const long long INF = 1LL << 60;
typedef vector<ll> Array;
typedef vector<Array> Matrix;

// sortは初期で昇順 greater<hoge>()で降順
// substr　文字列取り出し
// upper_bound
// ある値より大きい一番左のイテレータを返す、lowerは以上(setに対して使うとO(N)なので、setのメンバ関数を使う
// stoi

struct Edge { // グラフ
  ll to, cap, rev;
  Edge(ll _to, ll _cap, ll _rev) {
    to = _to;
    cap = _cap;
    rev = _rev;
  }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
void add_edge(Graph &G, ll from, ll to,
              ll cap) { // 最大フロー求める Ford-fulkerson
  G[from].push_back(Edge(to, cap, (ll)G[to].size()));
  G[to].push_back(
      Edge(from, cap, (ll)G[from].size() - 1)); // 最小カットの場合逆辺は0にする
}
ll max_flow_dfs(Graph &G, ll v, ll t, ll f, vector<bool> &used) {
  if (v == t)
    return f;
  used[v] = true;
  for (int i = 0; i < G[v].size(); ++i) {
    Edge &e = G[v][i];
    if (!used[e.to] && e.cap > 0) {
      ll d = max_flow_dfs(G, e.to, t, min(f, e.cap), used);
      if (d > 0) {
        e.cap -= d;
        G[e.to][e.rev].cap += d;
        return d;
      }
    }
  }
  return 0;
}
ll max_flow(Graph &G, ll s, ll t) {
  ll flow = 0;
  for (;;) {
    vector<bool> used(G.size());
    REP(i, used.size()) used[i] = false;
    ll f = max_flow_dfs(G, s, t, INF, used);
    if (f == 0) {
      return flow;
    }
    flow += f;
  }
}

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

class UnionFind {
  vector<int> data;

public:
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

// 約数求める //約数
void divisor(ll n, vector<ll> &ret) {
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end());
}

// nCrとか
class Combination {
public:
  Array fact;
  Array inv;
  ll mod;
  ll mod_inv(ll x) {
    ll n = mod - 2;
    ll res = 1LL;
    while (n > 0) {
      if (n & 1)
        res = res * x % mod;
      x = x * x % mod;
      n >>= 1;
    }
    return res;
  }
  ll nCr(ll n, ll r) { return ((fact[n] * inv[r] % mod) * inv[n - r]) % mod; }
  ll nPr(ll n, ll r) { return (fact[n] * inv[n - r]) % mod; }
  Combination(ll n, ll _mod) {
    mod = _mod;
    fact.resize(n + 1);
    fact[0] = 1;
    REP(i, n) { fact[i + 1] = (fact[i] * (i + 1LL)) % mod; }
    inv.resize(n + 1);
    REP(i, n + 1) { inv[i] = mod_inv(fact[i]); }
  }
};

bool compare_by_b(pair<ll, ll> a, pair<ll, ll> b) { // 降順second
  if (a.second != b.second) {
    return a.second > b.second;
  } else {
    return a.first > b.first;
  }
}

bool compare_by_a(pair<ll, ll> a, pair<ll, ll> b) { // 降順first
  if (a.first != b.first) {
    return a.first > b.first;
  } else {
    return a.second > b.second;
  }
}

ll gcd(ll m, ll n) {
  if (n == 0)
    return m;
  return gcd(n, m % n);
} // gcd

ll lcm(ll m, ll n) { return m / gcd(m, n) * n; }

int used[10000];
int main() {
  ll h, w;
  cin >> h >> w;
  Graph graph(h * w + 1);
  vector<string> s(h);
  REP(i, h) { cin >> s[i]; }
  ll blk = 0;
  REP(i, h) {
    REP(j, w) {
      if (s[i][j] == '.') {
        if (j != w - 1 && s[i][j + 1] == '.') {
          add_edge(graph, i * w + j, i * w + j + 1, 0);
        }
        if (i != h - 1 && s[i + 1][j] == '.') {
          add_edge(graph, i * w + j, (i + 1LL) * w + j, 0);
        }
      } else {
        blk++;
      }
    }
  }
  queue<pair<ll, ll>> que;
  que.push(make_pair(0, 1));
  used[0] = 1;
  while (!que.empty()) {
    if (que.front().first == h * w - 1) {
      cout << h * w - blk - que.front().second;
      return 0;
    }

    REP(i, graph[que.front().first].size()) {
      if (used[graph[que.front().first][i].to] == 0) {
        que.push(
            make_pair(graph[que.front().first][i].to, que.front().second + 1));
        used[que.front().first] = 1;
      }
    }
    que.pop();
  }
  cout << -1;

  return 0;
}


Fixed submission:
/*
ll used[10];
ll maxi;

ll dfs(Graph& graph, ll v, ll deep) {
        used[v] = 1;
        vector<ll> maxd;
        maxd.push_back(deep);
        for (int i = 0; i < graph[v].size(); i++) {
                if (used[graph[v][i].to] == 0) {
                        maxd.push_back(dfs(graph, graph[v][i].to, deep + 1));
                }
        }
        sort(all(maxd), greater<ll>());
        if (maxd.size() > 2) {
                chmax(maxi, maxd[0] - deep + maxd[1] - deep);
        }
        else {
                chmax(maxi, maxd[0] - deep);
        }
        return maxd[0];
}
*///dfs
/*
REP(i, n) {
        REP(j, n) {
                dp[i][j] = INF;
        }
}
REP(i, m) {
        ll a, b, c;
        cin >> a >> b >> c;
        dp[a][b] = c;
        dp[b][a] = c;
}
REP(i, n) {
        REP(j, n) {
                REP(k, n) {
                        chmin(dp[j][k], dp[j][i] + dp[i][k]);
                }
        }
}
*///warshall floyd

#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
#define MOD 1000000007
#define REP(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define FOR(i, c)                                                              \
  for (decltype((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ll long long
#define ull unsigned long long
#define all(hoge) (hoge).begin(), (hoge).end()
const long long INF = 1LL << 60;
typedef vector<ll> Array;
typedef vector<Array> Matrix;

// sortは初期で昇順 greater<hoge>()で降順
// substr　文字列取り出し
// upper_bound
// ある値より大きい一番左のイテレータを返す、lowerは以上(setに対して使うとO(N)なので、setのメンバ関数を使う
// stoi

struct Edge { // グラフ
  ll to, cap, rev;
  Edge(ll _to, ll _cap, ll _rev) {
    to = _to;
    cap = _cap;
    rev = _rev;
  }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
void add_edge(Graph &G, ll from, ll to,
              ll cap) { // 最大フロー求める Ford-fulkerson
  G[from].push_back(Edge(to, cap, (ll)G[to].size()));
  G[to].push_back(
      Edge(from, cap, (ll)G[from].size() - 1)); // 最小カットの場合逆辺は0にする
}
ll max_flow_dfs(Graph &G, ll v, ll t, ll f, vector<bool> &used) {
  if (v == t)
    return f;
  used[v] = true;
  for (int i = 0; i < G[v].size(); ++i) {
    Edge &e = G[v][i];
    if (!used[e.to] && e.cap > 0) {
      ll d = max_flow_dfs(G, e.to, t, min(f, e.cap), used);
      if (d > 0) {
        e.cap -= d;
        G[e.to][e.rev].cap += d;
        return d;
      }
    }
  }
  return 0;
}
ll max_flow(Graph &G, ll s, ll t) {
  ll flow = 0;
  for (;;) {
    vector<bool> used(G.size());
    REP(i, used.size()) used[i] = false;
    ll f = max_flow_dfs(G, s, t, INF, used);
    if (f == 0) {
      return flow;
    }
    flow += f;
  }
}

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

class UnionFind {
  vector<int> data;

public:
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

// 約数求める //約数
void divisor(ll n, vector<ll> &ret) {
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end());
}

// nCrとか
class Combination {
public:
  Array fact;
  Array inv;
  ll mod;
  ll mod_inv(ll x) {
    ll n = mod - 2;
    ll res = 1LL;
    while (n > 0) {
      if (n & 1)
        res = res * x % mod;
      x = x * x % mod;
      n >>= 1;
    }
    return res;
  }
  ll nCr(ll n, ll r) { return ((fact[n] * inv[r] % mod) * inv[n - r]) % mod; }
  ll nPr(ll n, ll r) { return (fact[n] * inv[n - r]) % mod; }
  Combination(ll n, ll _mod) {
    mod = _mod;
    fact.resize(n + 1);
    fact[0] = 1;
    REP(i, n) { fact[i + 1] = (fact[i] * (i + 1LL)) % mod; }
    inv.resize(n + 1);
    REP(i, n + 1) { inv[i] = mod_inv(fact[i]); }
  }
};

bool compare_by_b(pair<ll, ll> a, pair<ll, ll> b) { // 降順second
  if (a.second != b.second) {
    return a.second > b.second;
  } else {
    return a.first > b.first;
  }
}

bool compare_by_a(pair<ll, ll> a, pair<ll, ll> b) { // 降順first
  if (a.first != b.first) {
    return a.first > b.first;
  } else {
    return a.second > b.second;
  }
}

ll gcd(ll m, ll n) {
  if (n == 0)
    return m;
  return gcd(n, m % n);
} // gcd

ll lcm(ll m, ll n) { return m / gcd(m, n) * n; }

int used[10000];
int main() {
  ll h, w;
  cin >> h >> w;
  Graph graph(h * w + 1);
  vector<string> s(h);
  REP(i, h) { cin >> s[i]; }
  ll blk = 0;
  REP(i, h) {
    REP(j, w) {
      if (s[i][j] == '.') {
        if (j != w - 1 && s[i][j + 1] == '.') {
          add_edge(graph, i * w + j, i * w + j + 1, 0);
        }
        if (i != h - 1 && s[i + 1][j] == '.') {
          add_edge(graph, i * w + j, (i + 1LL) * w + j, 0);
        }
      } else {
        blk++;
      }
    }
  }
  queue<pair<ll, ll>> que;
  que.push(make_pair(0, 1));
  used[0] = 1;
  while (!que.empty()) {
    if (que.front().first == h * w - 1) {
      cout << h * w - blk - que.front().second;
      return 0;
    }

    REP(i, graph[que.front().first].size()) {
      if (used[graph[que.front().first][i].to] == 0) {
        que.push(
            make_pair(graph[que.front().first][i].to, que.front().second + 1));
        used[graph[que.front().first][i].to] = 1;
      }
    }
    que.pop();
  }
  cout << -1;

  return 0;
}