Problem p03179 (C++)

Buggy submission (status: Runtime Error):
// {{{ by unolight
#include <bits/stdc++.h>
#include <unistd.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#define SZ(x) ((int)(x).size())
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define REP(i, n) for (int i = 0; i < int(n); i++)
#define REP1(i, a, b) for (int i = (a); i <= int(b); i++)
#define MP make_pair
#define PB push_back
using namespace std;
typedef int64_t LL;
typedef pair<int, int> PII;
typedef vector<int> VI;
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" PRId64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f\n", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
template <class T> inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T, class F = less<T>> void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
template <class T> using MaxHeap = priority_queue<T>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;
#ifdef UNO
template <class T> void _dump(const char *s, T &&head) {
  cerr << s << "=" << head << endl;
}
template <class T, class... Args>
void _dump(const char *s, T &&head, Args &&...tail) {
  for (int c = 0; *s != ',' || c != 0; cerr << *s++) {
    if (*s == '(' || *s == '[' || *s == '{')
      c++;
    if (*s == ')' || *s == ']' || *s == '}')
      c--;
  }
  cerr << "=" << head << ", ";
  _dump(s + 1, tail...);
}
#define dump(...)                                                              \
  do {                                                                         \
    fprintf(stderr, "%s:%d - ", __PRETTY_FUNCTION__, __LINE__);                \
    _dump(#__VA_ARGS__, __VA_ARGS__);                                          \
  } while (0)
template <class Iter> ostream &_out(ostream &s, Iter b, Iter e) {
  s << "[";
  for (auto it = b; it != e; it++)
    s << (it == b ? "" : " ") << *it;
  return s << "]";
}
template <class A, class B>
ostream &operator<<(ostream &s, const pair<A, B> &p) {
  return s << "(" << p.first << "," << p.second << ")";
}
template <class T> ostream &operator<<(ostream &s, const vector<T> &c) {
  return _out(s, ALL(c));
}
template <class T, size_t N>
ostream &operator<<(ostream &s, const array<T, N> &c) {
  return _out(s, ALL(c));
}
template <class T> ostream &operator<<(ostream &s, const set<T> &c) {
  return _out(s, ALL(c));
}
template <class A, class B>
ostream &operator<<(ostream &s, const map<A, B> &c) {
  return _out(s, ALL(c));
}
#else
#define dump(...)
#endif
// }}}

// {{{ ModInt
template <int _MOD> struct ModInt {
  static const auto MOD = _MOD;
  template <class T>
  using integral_only = typename enable_if<is_integral<T>::value>::type;
  int x;
  constexpr ModInt() : x() {}
  template <class T, integral_only<T> * = nullptr> ModInt(T _x = 0) {
    x = _x % MOD;
    if (x < 0)
      x += MOD;
  }
  ModInt operator-() const { return {x == 0 ? 0 : MOD - x}; }
  ModInt &operator+=(const ModInt a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt a) {
    x = (long long)x * a.x % MOD;
    return *this;
  }
  ModInt &operator/=(const ModInt a) { return (*this) *= a.inv(); }
  ModInt operator+(const ModInt a) const { return ModInt(*this) += a; }
  ModInt operator-(const ModInt a) const { return ModInt(*this) -= a; }
  ModInt operator*(const ModInt a) const { return ModInt(*this) *= a; }
  ModInt operator/(const ModInt a) const { return ModInt(*this) /= a; }
  ModInt inv() const {
    // for prime MOD
    return pow(MOD - 2);
  }
  ModInt inv2() const {
    // work for non-prime MOD if gcd(x,MOD) = 1
    int a = x, b = MOD, u = 1, v = 0;
    while (b != 0) {
      int t = a / b;
      a -= t * b;
      u -= t * v;
      swap(a, b);
      swap(u, v);
    }
    return u;
  }
  template <class T, integral_only<T> * = nullptr> ModInt pow(T t) const {
    ModInt r = 1, p = *this;
    while (t) {
      if (t & 1)
        r *= p;
      p *= p;
      t >>= 1;
    }
    return r;
  }
  bool operator==(ModInt rhs) const { return x == rhs.x; }
  bool operator!=(ModInt rhs) const { return x != rhs.x; }
  bool operator<(ModInt rhs) const { return x < rhs.x; }
  bool operator<=(ModInt rhs) const { return x <= rhs.x; }
  bool operator>(ModInt rhs) const { return x > rhs.x; }
  bool operator>=(ModInt rhs) const { return x >= rhs.x; }
  friend string to_string(ModInt i) { return to_string(i.x); }
  friend istream &operator>>(istream &i, ModInt &a) { return i >> a.x; }
  friend ostream &operator<<(ostream &o, const ModInt &a) { return o << a.x; }
};
const int MOD = 1000000007;
using mint = ModInt<MOD>;
// }}}

int main() {
  int n;
  R(n);
  string s;
  R(s);
  vector<mint> dp(1);
  dp[0] = 1;
  for (int i = 1; i < n; i++) {
    vector<mint> ndp(i + 1);
    if (s[i - 1] == '<') {
      mint sum = 0;
      for (int j = 0; j < i; j++) {
        sum += dp[j];
        ndp[j + 1] = sum;
      }
    } else {
      mint sum = 0;
      for (int j = i - 1; i >= 0; j--) {
        sum += dp[j];
        ndp[j] = sum;
      }
    }
    swap(dp, ndp);
  }
  cout << accumulate(ALL(dp), mint(0)) << '\n';
  return 0;
}


Fixed submission:
// {{{ by unolight
#include <bits/stdc++.h>
#include <unistd.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#define SZ(x) ((int)(x).size())
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define REP(i, n) for (int i = 0; i < int(n); i++)
#define REP1(i, a, b) for (int i = (a); i <= int(b); i++)
#define MP make_pair
#define PB push_back
using namespace std;
typedef int64_t LL;
typedef pair<int, int> PII;
typedef vector<int> VI;
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" PRId64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f\n", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
template <class T> inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T, class F = less<T>> void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
template <class T> using MaxHeap = priority_queue<T>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;
#ifdef UNO
template <class T> void _dump(const char *s, T &&head) {
  cerr << s << "=" << head << endl;
}
template <class T, class... Args>
void _dump(const char *s, T &&head, Args &&...tail) {
  for (int c = 0; *s != ',' || c != 0; cerr << *s++) {
    if (*s == '(' || *s == '[' || *s == '{')
      c++;
    if (*s == ')' || *s == ']' || *s == '}')
      c--;
  }
  cerr << "=" << head << ", ";
  _dump(s + 1, tail...);
}
#define dump(...)                                                              \
  do {                                                                         \
    fprintf(stderr, "%s:%d - ", __PRETTY_FUNCTION__, __LINE__);                \
    _dump(#__VA_ARGS__, __VA_ARGS__);                                          \
  } while (0)
template <class Iter> ostream &_out(ostream &s, Iter b, Iter e) {
  s << "[";
  for (auto it = b; it != e; it++)
    s << (it == b ? "" : " ") << *it;
  return s << "]";
}
template <class A, class B>
ostream &operator<<(ostream &s, const pair<A, B> &p) {
  return s << "(" << p.first << "," << p.second << ")";
}
template <class T> ostream &operator<<(ostream &s, const vector<T> &c) {
  return _out(s, ALL(c));
}
template <class T, size_t N>
ostream &operator<<(ostream &s, const array<T, N> &c) {
  return _out(s, ALL(c));
}
template <class T> ostream &operator<<(ostream &s, const set<T> &c) {
  return _out(s, ALL(c));
}
template <class A, class B>
ostream &operator<<(ostream &s, const map<A, B> &c) {
  return _out(s, ALL(c));
}
#else
#define dump(...)
#endif
// }}}

// {{{ ModInt
template <int _MOD> struct ModInt {
  static const auto MOD = _MOD;
  template <class T>
  using integral_only = typename enable_if<is_integral<T>::value>::type;
  int x;
  constexpr ModInt() : x() {}
  template <class T, integral_only<T> * = nullptr> ModInt(T _x = 0) {
    x = _x % MOD;
    if (x < 0)
      x += MOD;
  }
  ModInt operator-() const { return {x == 0 ? 0 : MOD - x}; }
  ModInt &operator+=(const ModInt a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt a) {
    x = (long long)x * a.x % MOD;
    return *this;
  }
  ModInt &operator/=(const ModInt a) { return (*this) *= a.inv(); }
  ModInt operator+(const ModInt a) const { return ModInt(*this) += a; }
  ModInt operator-(const ModInt a) const { return ModInt(*this) -= a; }
  ModInt operator*(const ModInt a) const { return ModInt(*this) *= a; }
  ModInt operator/(const ModInt a) const { return ModInt(*this) /= a; }
  ModInt inv() const {
    // for prime MOD
    return pow(MOD - 2);
  }
  ModInt inv2() const {
    // work for non-prime MOD if gcd(x,MOD) = 1
    int a = x, b = MOD, u = 1, v = 0;
    while (b != 0) {
      int t = a / b;
      a -= t * b;
      u -= t * v;
      swap(a, b);
      swap(u, v);
    }
    return u;
  }
  template <class T, integral_only<T> * = nullptr> ModInt pow(T t) const {
    ModInt r = 1, p = *this;
    while (t) {
      if (t & 1)
        r *= p;
      p *= p;
      t >>= 1;
    }
    return r;
  }
  bool operator==(ModInt rhs) const { return x == rhs.x; }
  bool operator!=(ModInt rhs) const { return x != rhs.x; }
  bool operator<(ModInt rhs) const { return x < rhs.x; }
  bool operator<=(ModInt rhs) const { return x <= rhs.x; }
  bool operator>(ModInt rhs) const { return x > rhs.x; }
  bool operator>=(ModInt rhs) const { return x >= rhs.x; }
  friend string to_string(ModInt i) { return to_string(i.x); }
  friend istream &operator>>(istream &i, ModInt &a) { return i >> a.x; }
  friend ostream &operator<<(ostream &o, const ModInt &a) { return o << a.x; }
};
const int MOD = 1000000007;
using mint = ModInt<MOD>;
// }}}

int main() {
  int n;
  R(n);
  string s;
  R(s);
  vector<mint> dp(1);
  dp[0] = 1;
  for (int i = 1; i < n; i++) {
    vector<mint> ndp(i + 1);
    if (s[i - 1] == '<') {
      mint sum = 0;
      for (int j = 0; j < i; j++) {
        sum += dp[j];
        ndp[j + 1] = sum;
      }
    } else {
      mint sum = 0;
      for (int j = i - 1; j >= 0; j--) {
        sum += dp[j];
        ndp[j] = sum;
      }
    }
    swap(dp, ndp);
  }
  cout << accumulate(ALL(dp), mint(0)) << '\n';
  return 0;
}