Problem p00860 (C++)

Buggy submission (status: Time Limit Exceeded):

#include <bits/stdc++.h>
using namespace std;
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
#define all(v) v.begin(), v.end()

const int INF = 1 << 30;
const int dx[] = {0, 1, 0, -1, 0};
const int dy[] = {1, 0, -1, 0, 0};

struct State {
  array<int, 3> xs, ys;
  State() {
    fill(all(xs), 0);
    fill(all(ys), 0);
  }
  int hash() {
    int a = 0;
    rep(i, 3) a = a | (xs[i] << (4 * i));
    rep(i, 3) a = a | (ys[i] << (4 * i + 4 * 3));
    return a;
  }
};

array<short, 1 << 24> dist;

bool solve() {
  int W, H, N;
  vector<string> G;
  cin >> W >> H >> N;
  if (W == 0)
    return false;
  cin.ignore();
  rep(i, H) {
    string s;
    getline(cin, s);
    G.push_back(s);
  }
  State init, last;

  rep(y, H) rep(x, W) {
    int i = G[y][x] - 'a';
    int j = G[y][x] - 'A';
    if (0 <= i and i < N) {
      init.ys[i] = y;
      init.xs[i] = x;
    }
    if (0 <= j and j < N) {
      last.ys[j] = y;
      last.xs[j] = x;
    }
  }

  auto on_field = [&](int y, int x) {
    return 0 <= y and y < H and 0 <= x and x < W and G[y][x] != '#';
  };
  auto move = [&](State &s, int idx, int dir) {
    s.xs[idx] += dx[dir];
    s.ys[idx] += dy[dir];
    return on_field(s.ys[idx], s.xs[idx]);
  };
  auto same = [&](State &s, int i) {
    rep(j, i) {
      if (s.ys[i] == s.ys[j] and s.xs[i] == s.xs[j])
        return true;
    }
    return false;
  };
  auto swapped = [&](State &n, State &p) {
    rep(i, N) rep(j, N) if (i != j) {
      if ((n.ys[j] == p.ys[i] and n.xs[j] == p.xs[i]) and
          (n.ys[i] == p.ys[j] and n.xs[i] == p.xs[j]))
        return true;
    }
    return false;
  };

  int last_hash = last.hash();

  queue<State> que;
  fill(all(dist), -1);
  que.push(init);
  dist[init.hash()] = 0;
  while (que.size()) {
    State now = que.front();
    que.pop();
    int nh = now.hash();
    rep(i, 5) {
      State nxt1 = now;
      if (not move(nxt1, 0, i))
        continue;
      rep(j, 5) {
        State nxt2 = nxt1;
        if (N >= 2 and not move(nxt2, 1, j))
          continue;
        if (N >= 2 and same(nxt2, 1))
          continue;
        rep(k, 5) {
          State nxt3 = nxt2;
          if (N >= 3 and not move(nxt3, 2, k))
            continue;
          if (N >= 3 and same(nxt3, 2))
            continue;

          if (not swapped(nxt3, now)) {
            int h = nxt3.hash();
            if (last_hash == h) {
              cout << dist[nh] + 1 << endl;
              return 1;
            }
            if (dist[h] < 0) {
              dist[h] = dist[nh] + 1;
              que.push(nxt3);
            }
          }
        }
      }
    }
  }
  assert(0);
  return 1;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  while (solve())
    ;
  return 0;
}

Fixed submission:
#pragma GCC optimize "O3"
#include <bits/stdc++.h>
using namespace std;
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
#define all(v) v.begin(), v.end()

const int INF = 1 << 30;
const int dx[] = {0, 1, 0, -1, 0};
const int dy[] = {1, 0, -1, 0, 0};

struct State {
  array<int, 3> xs, ys;
  State() {
    fill(all(xs), 0);
    fill(all(ys), 0);
  }
  int hash() {
    int a = 0;
    rep(i, 3) a = a | (xs[i] << (4 * i));
    rep(i, 3) a = a | (ys[i] << (4 * i + 4 * 3));
    return a;
  }
};

array<short, 1 << 24> dist;

bool solve() {
  int W, H, N;
  vector<string> G;
  cin >> W >> H >> N;
  if (W == 0)
    return false;
  cin.ignore();
  rep(i, H) {
    string s;
    getline(cin, s);
    G.push_back(s);
  }
  State init, last;

  rep(y, H) rep(x, W) {
    int i = G[y][x] - 'a';
    int j = G[y][x] - 'A';
    if (0 <= i and i < N) {
      init.ys[i] = y;
      init.xs[i] = x;
    }
    if (0 <= j and j < N) {
      last.ys[j] = y;
      last.xs[j] = x;
    }
  }

  auto on_field = [&](int y, int x) {
    return 0 <= y and y < H and 0 <= x and x < W and G[y][x] != '#';
  };
  auto move = [&](State &s, int idx, int dir) {
    s.xs[idx] += dx[dir];
    s.ys[idx] += dy[dir];
    return on_field(s.ys[idx], s.xs[idx]);
  };
  auto same = [&](State &s, int i) {
    rep(j, i) {
      if (s.ys[i] == s.ys[j] and s.xs[i] == s.xs[j])
        return true;
    }
    return false;
  };
  auto swapped = [&](State &n, State &p) {
    rep(i, N) rep(j, N) if (i != j) {
      if ((n.ys[j] == p.ys[i] and n.xs[j] == p.xs[i]) and
          (n.ys[i] == p.ys[j] and n.xs[i] == p.xs[j]))
        return true;
    }
    return false;
  };

  int last_hash = last.hash();

  queue<State> que;
  fill(all(dist), -1);
  que.push(init);
  dist[init.hash()] = 0;
  while (que.size()) {
    State now = que.front();
    que.pop();
    int nh = now.hash();
    rep(i, 5) {
      State nxt1 = now;
      if (not move(nxt1, 0, i))
        continue;
      rep(j, 5) {
        State nxt2 = nxt1;
        if (N >= 2 and not move(nxt2, 1, j))
          continue;
        if (N >= 2 and same(nxt2, 1))
          continue;
        rep(k, 5) {
          State nxt3 = nxt2;
          if (N >= 3 and not move(nxt3, 2, k))
            continue;
          if (N >= 3 and same(nxt3, 2))
            continue;

          if (not swapped(nxt3, now)) {
            int h = nxt3.hash();
            if (last_hash == h) {
              cout << dist[nh] + 1 << endl;
              return 1;
            }
            if (dist[h] < 0) {
              dist[h] = dist[nh] + 1;
              que.push(nxt3);
            }
          }
        }
      }
    }
  }
  assert(0);
  return 1;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  while (solve())
    ;
  return 0;
}