Problem p03429 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

#define int long long
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CINT(...)                                                              \
  int __VA_ARGS__;                                                             \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  ll __VA_ARGS__;                                                              \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
  {                                                                            \
    FOREACH(x, v) { cout << x << " "; }                                        \
    cout << "\n";                                                              \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef unsigned long long ul;
typedef vector<ll> VL;
typedef pair<ll, ll> PL;

const int INF = 1e9;
const int MOD = 1e9 + 7;
const double PI = atan(1.0) * 4.0;
// const int MOD = 998244353;
const ll LINF = 9e18;
const ll dx[] = {1, 0, -1, 0};
const ll dy[] = {0, 1, 0, -1};

ll H, W, A, B;
string S[1009];

signed main() {
  cin >> H >> W >> A >> B;
  if (H * W < 2 * (A + B))
    eputs("NO");
  FOR(i, 1, H + 1) FOR(j, 1, W + 1) S[i][j] = '.';
  if (H % 2) {
    for (int i = 1; i < W and A; i += 2)
      S[H][i] = '<', S[H][i + 1] = '>', A--;
  }
  if (W % 2) {
    for (int i = 1; i < H and B; i += 2)
      S[i][W] = '^', S[i + 1][W] = 'v', B--;
  }
  for (int i = 1; i < H; i += 2)
    for (int j = 1; j < W; j += 2) {
      if (A >= 2) {
        S[i][j] = '<', S[i][j + 1] = '>';
        S[i + 1][j] = '<', S[i + 1][j + 1] = '>';
        A -= 2;
      } else if (B >= 2) {
        S[i][j] = '^', S[i][j + 1] = '^';
        S[i + 1][j] = 'v', S[i + 1][j + 1] = 'v';
        B -= 2;
      } else if (A && B && i == H - 2 && j == W - 2) {
        A--, B--;
        S[i][j] = '<', S[i][j + 1] = '>', S[i][j + 2] = '^';
        S[i + 1][j] = '^', S[i + 1][j + 2] = 'v';
        S[i + 2][j] = 'v', S[i + 2][j + 1] = '<', S[i + 2][j + 2] = '>';
      } else if (A) {
        A--;
        S[i][j] = '<', S[i][j + 1] = '>';
      } else if (B) {
        B--;
        S[i][j] = '^', S[i + 1][j] = 'v';
      }
    }
  if (A || B)
    eputs("NO");
  puts("YES");
  FOR(i, 1, H + 1) {
    FOR(j, 1, W + 1) cout << S[i][j];
    cout << "\n";
  }
}

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

using namespace std;

#define int long long
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CINT(...)                                                              \
  int __VA_ARGS__;                                                             \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  ll __VA_ARGS__;                                                              \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
  {                                                                            \
    FOREACH(x, v) { cout << x << " "; }                                        \
    cout << "\n";                                                              \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef unsigned long long ul;
typedef vector<ll> VL;
typedef pair<ll, ll> PL;

const int INF = 1e9;
const int MOD = 1e9 + 7;
const double PI = atan(1.0) * 4.0;
// const int MOD = 998244353;
const ll LINF = 9e18;
const ll dx[] = {1, 0, -1, 0};
const ll dy[] = {0, 1, 0, -1};

ll H, W, A, B;
char S[1009][1009];

signed main() {
  cin >> H >> W >> A >> B;
  if (H * W < 2 * (A + B))
    eputs("NO");
  FOR(i, 1, H + 1) FOR(j, 1, W + 1) S[i][j] = '.';
  if (H % 2) {
    for (int i = 1; i < W and A; i += 2)
      S[H][i] = '<', S[H][i + 1] = '>', A--;
  }
  if (W % 2) {
    for (int i = 1; i < H and B; i += 2)
      S[i][W] = '^', S[i + 1][W] = 'v', B--;
  }
  for (int i = 1; i < H; i += 2)
    for (int j = 1; j < W; j += 2) {
      if (A >= 2) {
        S[i][j] = '<', S[i][j + 1] = '>';
        S[i + 1][j] = '<', S[i + 1][j + 1] = '>';
        A -= 2;
      } else if (B >= 2) {
        S[i][j] = '^', S[i][j + 1] = '^';
        S[i + 1][j] = 'v', S[i + 1][j + 1] = 'v';
        B -= 2;
      } else if (A && B && i == H - 2 && j == W - 2) {
        A--, B--;
        S[i][j] = '<', S[i][j + 1] = '>', S[i][j + 2] = '^';
        S[i + 1][j] = '^', S[i + 1][j + 2] = 'v';
        S[i + 2][j] = 'v', S[i + 2][j + 1] = '<', S[i + 2][j + 2] = '>';
      } else if (A) {
        A--;
        S[i][j] = '<', S[i][j + 1] = '>';
      } else if (B) {
        B--;
        S[i][j] = '^', S[i + 1][j] = 'v';
      }
    }
  if (A || B)
    eputs("NO");
  puts("YES");
  FOR(i, 1, H + 1) {
    FOR(j, 1, W + 1) cout << S[i][j];
    cout << "\n";
  }
}