Problem p00918 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

const int N = 3;
int start[N][N], goal[N][N];

using State = tuple<int, string>;

int main(void) {
  for (int cx, cy; cin >> cx >> cy, cx;) {
    rep(i, N) rep(j, N) cin >> start[i][j];
    rep(i, N) rep(j, N) cin >> goal[i][j];

    auto vec2s = [&](int hoge[N][N]) {
      string ret;
      rep(i, N) {
        rep(j, N) { ret += to_string(hoge[i][j]); }
      }
      return ret;
    };

    string s = vec2s(start);
    string z = vec2s(goal);

    priority_queue<State, vector<State>, greater<State>> q;
    q.push(State(0, s));

    map<string, int> min_cost;

    int res = -1;
    while (q.size()) {
      int cost;
      string f;
      tie(cost, f) = q.top(), q.pop();

      if (min_cost.find(f) != end(min_cost))
        continue;
      min_cost[f] = cost;

      if (f == z) {
        res = cost;
        break;
      }

      int bx = -1, by = -1;
      rep(i, N * N) {
        if (f[i] == '0') {
          bx = i % 3, by = i / 3;
          break;
        }
      }
      assert(bx != -1 and by != -1);

      rep(i, 4) {
        int tx = bx + dx[i], ty = (by + dy[i] + N) % N;

        if (tx < 0) {
          tx = 2;
          ty = (by + 2) % N;
        } else if (tx >= N) {
          tx = 0;
          ty = (by + 1) % N;
        }

        assert(not(tx < 0 or N <= tx or ty < 0 or N <= ty));

        string nf = f;
        swap(nf[ty * 3 + tx], nf[by * 3 + bx]);
        int ncost = cost + (i % 2 == 0 ? cx : cy);
        if (min_cost.find(nf) == end(min_cost)) {
          q.push(State(ncost, nf));
        }
      }
    }

    cout << res << endl;
  }

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

const int N = 3;
int start[N][N], goal[N][N];

using State = tuple<int, string>;

int main(void) {
  for (int cx, cy; cin >> cx >> cy, cx;) {
    rep(i, N) rep(j, N) cin >> start[i][j];
    rep(i, N) rep(j, N) cin >> goal[i][j];

    auto vec2s = [&](int hoge[N][N]) {
      string ret;
      rep(i, N) {
        rep(j, N) { ret += to_string(hoge[i][j]); }
      }
      return ret;
    };

    string s = vec2s(start);
    string z = vec2s(goal);

    priority_queue<State, vector<State>, greater<State>> q;
    q.push(State(0, s));

    unordered_map<string, int> min_cost;

    int res = -1;
    while (q.size()) {
      int cost;
      string f;
      tie(cost, f) = q.top(), q.pop();

      if (min_cost.find(f) != end(min_cost))
        continue;
      min_cost[f] = cost;

      if (f == z) {
        res = cost;
        break;
      }

      int bx = -1, by = -1;
      rep(i, N * N) {
        if (f[i] == '0') {
          bx = i % 3, by = i / 3;
          break;
        }
      }
      assert(bx != -1 and by != -1);

      rep(i, 4) {
        int tx = bx + dx[i], ty = (by + dy[i] + N) % N;

        if (tx < 0) {
          tx = 2;
          ty = (by + 2) % N;
        } else if (tx >= N) {
          tx = 0;
          ty = (by + 1) % N;
        }

        assert(not(tx < 0 or N <= tx or ty < 0 or N <= ty));

        string nf = f;
        swap(nf[ty * 3 + tx], nf[by * 3 + bx]);
        int ncost = cost + (i % 2 == 0 ? cx : cy);
        if (min_cost.find(nf) == end(min_cost)) {
          q.push(State(ncost, nf));
        }
      }
    }

    cout << res << endl;
  }

  return 0;
}