Problem p03859 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)
#define all(x) (x).begin(), (x).end()
#define dump(x) cerr << #x << " = " << (x) << endl;
template <typename T> using V = vector<T>;
template <typename T> using P = pair<T, T>;
using Vi = V<int>;
using Vl = V<ll>;
using Vd = V<ld>;
using Vb = V<bool>;
using VVi = V<Vi>;
using VVl = V<Vl>;
using VVb = V<Vb>;
using Pi = P<int>;
using Pl = P<ll>;
using Pd = P<ld>;
template <typename T> vector<T> make_vec(size_t n, T a) {
  return vector<T>(n, a);
}
template <typename... Ts> auto make_vec(size_t n, Ts... ts) {
  return vector<decltype(make_vec(ts...))>(n, make_vec(ts...));
}
template <typename T> inline int sz(T &x) { return x.size(); }
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << '(' << p.first << ", " << p.second << ')';
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << ' ';
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int cDiv(const ll x, const ll y) { return (x + y - 1) / y; } // ceil(x/y)
inline int fLog2(const ll x) {
  assert(x > 0);
  return 63 - __builtin_clzll(x);
} // floor(log2(x))
inline int cLog2(const ll x) {
  assert(x > 0);
  return (x == 1) ? 0 : 64 - __builtin_clzll(x - 1);
} // ceil(log2(x))
inline int popcount(const ll x) { return __builtin_popcountll(x); }
inline void fail() {
  cout << -1 << '\n';
  exit(0);
}
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
// const int INF  = 1<<30;
// const ll INFll = 1ll<<60;
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const int MOD = int(1e9) + 7;
// const int MOD  = 998244353;

template <int MOD> struct ModInt {
  int x;
  ModInt(ll _x = 0) : x((0 <= _x && _x < MOD) ? _x : (_x % MOD + MOD) % MOD) {}
  constexpr int &value() noexcept { return x; }
  constexpr ModInt operator-() const noexcept { return ModInt(MOD - x); }
  constexpr ModInt operator+(const ModInt y) const noexcept {
    return ModInt(*this) += y;
  }
  constexpr ModInt operator-(const ModInt y) const noexcept {
    return ModInt(*this) -= y;
  }
  constexpr ModInt operator*(const ModInt y) const noexcept {
    return ModInt(*this) *= y;
  }
  constexpr ModInt operator/(const ModInt y) const noexcept {
    return ModInt(*this) /= y;
  }
  constexpr ModInt &operator+=(const ModInt y) noexcept {
    x += y.x;
    if (x >= MOD)
      x -= MOD;
    return *this;
  }
  constexpr ModInt &operator-=(const ModInt y) noexcept {
    x -= y.x;
    if (x < 0)
      x += MOD;
    return *this;
  }
  constexpr ModInt &operator*=(const ModInt y) noexcept {
    x = ll(x) * y.x % MOD;
    return *this;
  }
  constexpr ModInt &operator/=(const ModInt y) {
    int a = y.x, b = MOD, u = 1, v = 0;
    while (b) {
      int t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    x = ll(x) * u % MOD;
    if (x < 0)
      x += MOD;
    return *this;
  }
  constexpr ModInt pow(ll n) const noexcept {
    ModInt x(1);
    ModInt a = *this;
    for (; n > 0; n >>= 1, a *= a)
      if (n & 1)
        x *= a;
    return x;
  }
};
using mint = ModInt<MOD>;
using Vm = vector<mint>;
using VVm = vector<Vm>;
using VVVm = vector<VVm>;
// istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

int main() {
  int n, m;
  cin >> n >> m;

  string s;
  cin >> s;
  V<Pi> lr(m);
  cin >> lr;
  rep(i, m)-- lr[i].first;

  auto t1 = s;
  auto t2 = s;
  for (auto [l, r] : lr)
    sort(t1.begin() + l, t1.begin() + r);
  for (auto [l, r] : lr)
    sort(t2.begin() + l, t2.begin() + r,
         [](auto &i, auto &j) { return i > j; });

  Vi lm, rm;
  rep(i, n) if (t1[i] == '0') lm.push_back(i);
  rep(i, n) if (t2[i] == '0') rm.push_back(i);

  Vm dp(n + 1);
  dp[0] = 1;
  rep(i, sz(lm)) {
    Vm tmp(n + 1);
    rep(j, lm[i] + 1) tmp[lm[i] + 1] += dp[j];
    rep2(j, lm[i] + 1, rm[i] + 1) tmp[j + 1] = tmp[j] + dp[j];
    swap(dp, tmp);
    dump(dp);
  }

  mint ans = 0;
  rep(i, n + 1) ans += dp[i];
  cout << ans << '\n';
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)
#define all(x) (x).begin(), (x).end()
#define dump(x) cerr << #x << " = " << (x) << endl;
template <typename T> using V = vector<T>;
template <typename T> using P = pair<T, T>;
using Vi = V<int>;
using Vl = V<ll>;
using Vd = V<ld>;
using Vb = V<bool>;
using VVi = V<Vi>;
using VVl = V<Vl>;
using VVb = V<Vb>;
using Pi = P<int>;
using Pl = P<ll>;
using Pd = P<ld>;
template <typename T> vector<T> make_vec(size_t n, T a) {
  return vector<T>(n, a);
}
template <typename... Ts> auto make_vec(size_t n, Ts... ts) {
  return vector<decltype(make_vec(ts...))>(n, make_vec(ts...));
}
template <typename T> inline int sz(T &x) { return x.size(); }
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << '(' << p.first << ", " << p.second << ')';
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << ' ';
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int cDiv(const ll x, const ll y) { return (x + y - 1) / y; } // ceil(x/y)
inline int fLog2(const ll x) {
  assert(x > 0);
  return 63 - __builtin_clzll(x);
} // floor(log2(x))
inline int cLog2(const ll x) {
  assert(x > 0);
  return (x == 1) ? 0 : 64 - __builtin_clzll(x - 1);
} // ceil(log2(x))
inline int popcount(const ll x) { return __builtin_popcountll(x); }
inline void fail() {
  cout << -1 << '\n';
  exit(0);
}
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
// const int INF  = 1<<30;
// const ll INFll = 1ll<<60;
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const int MOD = int(1e9) + 7;
// const int MOD  = 998244353;

template <int MOD> struct ModInt {
  int x;
  ModInt(ll _x = 0) : x((0 <= _x && _x < MOD) ? _x : (_x % MOD + MOD) % MOD) {}
  constexpr int &value() noexcept { return x; }
  constexpr ModInt operator-() const noexcept { return ModInt(MOD - x); }
  constexpr ModInt operator+(const ModInt y) const noexcept {
    return ModInt(*this) += y;
  }
  constexpr ModInt operator-(const ModInt y) const noexcept {
    return ModInt(*this) -= y;
  }
  constexpr ModInt operator*(const ModInt y) const noexcept {
    return ModInt(*this) *= y;
  }
  constexpr ModInt operator/(const ModInt y) const noexcept {
    return ModInt(*this) /= y;
  }
  constexpr ModInt &operator+=(const ModInt y) noexcept {
    x += y.x;
    if (x >= MOD)
      x -= MOD;
    return *this;
  }
  constexpr ModInt &operator-=(const ModInt y) noexcept {
    x -= y.x;
    if (x < 0)
      x += MOD;
    return *this;
  }
  constexpr ModInt &operator*=(const ModInt y) noexcept {
    x = ll(x) * y.x % MOD;
    return *this;
  }
  constexpr ModInt &operator/=(const ModInt y) {
    int a = y.x, b = MOD, u = 1, v = 0;
    while (b) {
      int t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    x = ll(x) * u % MOD;
    if (x < 0)
      x += MOD;
    return *this;
  }
  constexpr ModInt pow(ll n) const noexcept {
    ModInt x(1);
    ModInt a = *this;
    for (; n > 0; n >>= 1, a *= a)
      if (n & 1)
        x *= a;
    return x;
  }
};
using mint = ModInt<MOD>;
using Vm = vector<mint>;
using VVm = vector<Vm>;
using VVVm = vector<VVm>;
// istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

int main() {
  int n, m;
  cin >> n >> m;

  string s;
  cin >> s;
  V<Pi> lr(m);
  cin >> lr;
  rep(i, m)-- lr[i].first;

  auto t1 = s;
  auto t2 = s;
  for (auto [l, r] : lr)
    sort(t1.begin() + l, t1.begin() + r);
  for (auto [l, r] : lr)
    sort(t2.begin() + l, t2.begin() + r,
         [](auto &i, auto &j) { return i > j; });

  Vi lm, rm;
  rep(i, n) if (t1[i] == '0') lm.push_back(i);
  rep(i, n) if (t2[i] == '0') rm.push_back(i);

  Vm dp(n + 1);
  dp[0] = 1;
  rep(i, sz(lm)) {
    Vm tmp(n + 1);
    rep(j, lm[i] + 1) tmp[lm[i] + 1] += dp[j];
    rep2(j, lm[i] + 1, rm[i] + 1) tmp[j + 1] = tmp[j] + dp[j];
    swap(dp, tmp);
    // dump(dp);
  }

  mint ans = 0;
  rep(i, n + 1) ans += dp[i];
  cout << ans << '\n';
}