Problem p01956 (C++)

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

#define INF_LL (int64)1e18
#define INF (int32)1e9
#define REP(i, n) for (int64 i = 0; i < (n); i++)
#define FOR(i, a, b) for (int64 i = (a); i < (b); i++)
#define all(x) x.begin(), x.end()
#define fs first
#define sc second

using int32 = int_fast32_t;
using uint32 = uint_fast32_t;
using int64 = int_fast64_t;
using uint64 = uint_fast64_t;
using PII = pair<int32, int32>;
using PLL = pair<int64, int64>;

const double eps = 1e-10;

template <typename A, typename B> inline void chmin(A &a, B b) {
  if (a > b)
    a = b;
}
template <typename A, typename B> inline void chmax(A &a, B b) {
  if (a < b)
    a = b;
}

template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value != 0>::type fill_v(U &u, const V... v) {
  u = U(v...);
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value == 0>::type fill_v(U &u, const V... v) {
  for (auto &e : u)
    fill_v<T>(e, v...);
}

int main(void) {
  int64 N, H, W;
  cin >> N >> H >> W;
  vector<int64> x(N);
  REP(i, N) cin >> x[i];
  vector<int64> sum(N * W + 1, 0);
  REP(i, N) {
    if (i % 2 == 0) {
      sum[W * i + x[i]] += 1;
      sum[W * i + x[i] + W] += -1;
    } else {
      sum[W * i - x[i]] += -1;
      sum[W * i - x[i] - W] += 1;
    }
  }
  int64 res = 0;
  REP(i, N * W) sum[i + 1] += sum[i];
  REP(i, N * W) {
    if (sum[i] == 0)
      res += H;
  }
  cout << res << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define INF_LL (int64)1e18
#define INF (int32)1e9
#define REP(i, n) for (int64 i = 0; i < (n); i++)
#define FOR(i, a, b) for (int64 i = (a); i < (b); i++)
#define all(x) x.begin(), x.end()
#define fs first
#define sc second

using int32 = int_fast32_t;
using uint32 = uint_fast32_t;
using int64 = int_fast64_t;
using uint64 = uint_fast64_t;
using PII = pair<int32, int32>;
using PLL = pair<int64, int64>;

const double eps = 1e-10;

template <typename A, typename B> inline void chmin(A &a, B b) {
  if (a > b)
    a = b;
}
template <typename A, typename B> inline void chmax(A &a, B b) {
  if (a < b)
    a = b;
}

template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value != 0>::type fill_v(U &u, const V... v) {
  u = U(v...);
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value == 0>::type fill_v(U &u, const V... v) {
  for (auto &e : u)
    fill_v<T>(e, v...);
}

int main(void) {
  int64 N, H, W;
  cin >> N >> H >> W;
  vector<int64> x(N);
  REP(i, N) cin >> x[i];
  vector<int64> sum(N * W + 1, 0);
  REP(i, N) {
    if (i % 2 == 0) {
      sum[W * i + x[i]] += 1;
      sum[W * i + x[i] + W] += -1;
    } else {
      sum[W * i - x[i]] += 1;
      sum[W * i - x[i] + W] += -1;
    }
  }
  int64 res = 0;
  REP(i, N * W) sum[i + 1] += sum[i];
  REP(i, N * W) {
    if (sum[i] == 0)
      res += H;
  }
  cout << res << endl;
}