Problem p00742 (C++) — buggy submission, verdict: 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);

int n, m;
vll coef;

vi not_zero, used;

const int N = 1 << 10;

// [si, ti)
void dfs(int si, int ti, ll sum, unordered_map<ll, ll> occ[N]) {
  if (si == ti) {
    int s = 0;
    rep(i, 10) if (used[i]) s |= (1 << i);
    occ[s][sum]++;
    return;
  }

  rep(i, not_zero[si] ? 1 : 0, 10) {
    if (used[i])
      continue;
    used[i] = true;
    dfs(si + 1, ti, coef[si] * i + sum, occ);
    used[i] = false;
  }
}

int main(void) {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  for (; cin >> n, n;) {
    vector<string> nums(n);
    for (auto &e : nums)
      cin >> e;

    map<char, int> c2i;
    m = 0;
    rep(i, n) {
      for (auto &c : nums[i]) {
        if (c2i.find(c) == end(c2i)) {
          c2i[c] = m++;
        }
      }
    }
    not_zero = vi(m);
    for (auto &e : nums) {
      if (e.size() == 1)
        continue;
      int i = c2i[e.at(0)];
      not_zero[i] = true;
    }

    coef = vll(m);
    rep(i, n) {
      int len = nums[i].size();

      rep(j, len) {
        char c = nums[i][j];
        int idx = c2i[c];
        int sign = (i == n - 1 ? -1 : 1);
        coef[idx] += sign * (pow(10, len - 1 - j));
      }
    }

    unordered_map<ll, ll> occ1[N], occ2[N];
    int m1 = m / 2, m2 = m - m1;
    used.assign(10, false);
    dfs(0, m1, 0, occ1);
    used.assign(10, false);
    dfs(m1, m, 0, occ2);

    ll res = 0LL;
    rep(i, N) {
      for (auto &e : occ1[i]) {
        if (e.second == 0)
          continue;

        rep(j, N) {
          if ((i & j) != 0)
            continue;
          res += e.second * occ2[j][-e.first];
        }
      }
    }

    cout << res << endl;
  }

  return 0;
}

Error: TLE

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);

int n, m;
vll coef;

vi not_zero, used;

const int N = 1 << 10;

// [si, ti)
void dfs(int si, int ti, ll sum, map<ll, ll> occ[N]) {
  if (si == ti) {
    int s = 0;
    rep(i, 10) if (used[i]) s |= (1 << i);
    occ[s][sum]++;
    return;
  }

  rep(i, not_zero[si] ? 1 : 0, 10) {
    if (used[i])
      continue;
    used[i] = true;
    dfs(si + 1, ti, coef[si] * i + sum, occ);
    used[i] = false;
  }
}

int main(void) {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  for (; cin >> n, n;) {
    vector<string> nums(n);
    for (auto &e : nums)
      cin >> e;

    map<char, int> c2i;
    m = 0;
    rep(i, n) {
      for (auto &c : nums[i]) {
        if (c2i.find(c) == end(c2i)) {
          c2i[c] = m++;
        }
      }
    }
    not_zero = vi(m);
    for (auto &e : nums) {
      if (e.size() == 1)
        continue;
      int i = c2i[e.at(0)];
      not_zero[i] = true;
    }

    coef = vll(m);
    rep(i, n) {
      int len = nums[i].size();

      rep(j, len) {
        char c = nums[i][j];
        int idx = c2i[c];
        int sign = (i == n - 1 ? -1 : 1);
        coef[idx] += sign * (pow(10, len - 1 - j));
      }
    }

    map<ll, ll> occ1[N], occ2[N];
    int m1 = m / 2, m2 = m - m1;
    used.assign(10, false);
    dfs(0, m1, 0, occ1);
    used.assign(10, false);
    dfs(m1, m, 0, occ2);

    ll res = 0LL;
    rep(i, N) {
      for (auto &e : occ1[i]) {
        if (e.second == 0)
          continue;

        rep(j, N) {
          if ((i & j) != 0)
            continue;
          res += e.second * occ2[j][-e.first];
        }
      }
    }

    cout << res << endl;
  }

  return 0;
}