Problem p02917 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define INF 1 << 30
#define endl '\n'
#define maxn 100005
#define tc printf("Case %d: ", cs)
#define tcn printf("Case %d:\n", cs);
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);

#define dbg1(x) cerr << #x << " = " << x << endl;
#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
#define dbg3(x, y, z)                                                          \
  cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = "  \
       << z << endl;
#define dbg4(w, x, y, z)                                                       \
  cerr << #w << " = " << w << ", " << #x << " = " << x << ", " << #y << " = "  \
       << y << ", " << #z << " = " << z << endl;

template <typename F, typename S>
ostream &operator<<(ostream &os, const pair<F, S> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << *it;
  }
  return os << "}";
}

template <typename T> ostream &operator<<(ostream &os, const set<T> &v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << *it;
  }
  return os << "]";
}

template <typename F, typename S>
ostream &operator<<(ostream &os, const map<F, S> &v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}

#define dbg(args...)                                                           \
  do {                                                                         \
    cerr << #args << " : ";                                                    \
    faltu(args);                                                               \
  } while (0)

clock_t tStart = clock();
#define timeStamp                                                              \
  dbg("Execution Time: ", (double)(clock() - tStart) / CLOCKS_PER_SEC)

void faltu() { cerr << endl; }

template <typename T> void faltu(T a[], int n) {
  for (int i = 0; i < n; ++i)
    cerr << a[i] << ' ';
  cerr << endl;
}

template <typename T, typename... hello>
void faltu(T arg, const hello &...rest) {
  cerr << arg << ' ';
  faltu(rest...);
}
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    new_data_set;

/**___________________________________________________**/

int main() {
  FASTIO
  ///*
  // #ifndef ONLINE_JUDGE
  // 	freopen("in.txt", "r", stdin);
  // 	freopen("out.txt", "w", stdout);
  // 	freopen("error.txt", "w", stderr);
  // #endif
  //*/
  int T;
  // scanf("%d", &T);
  T = 1;
  for (int cs = 1; cs <= T; cs++) {
    int n;
    cin >> n;
    vector<int> a(n), b(n);
    for (int i = 0; i <= n; i++)
      b[i] = 1e9;
    for (int i = 0; i < n - 1; i++)
      cin >> a[i]; //, --a[i];

    for (int i = 0; i < n - 1; i++) {
      for (int j = i; j <= i + 1 && j + 1 < n; j++) {
        // dbg(i, b[j], a[i]);
        b[j] = min(b[j], a[i]);
        // dbg(i, b[j], a[i]);
      }
      // cerr << "--------------\n";
    }
    b[n - 1] = a[n - 2];
    int ans = 0;
    for (int i = 0; i < n; i++) {
      // dbg(b[i]);
      ans += b[i];
    }
    cout << ans << endl;
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define INF 1 << 30
#define endl '\n'
#define maxn 100005
#define tc printf("Case %d: ", cs)
#define tcn printf("Case %d:\n", cs);
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);

#define dbg1(x) cerr << #x << " = " << x << endl;
#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
#define dbg3(x, y, z)                                                          \
  cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = "  \
       << z << endl;
#define dbg4(w, x, y, z)                                                       \
  cerr << #w << " = " << w << ", " << #x << " = " << x << ", " << #y << " = "  \
       << y << ", " << #z << " = " << z << endl;

template <typename F, typename S>
ostream &operator<<(ostream &os, const pair<F, S> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << *it;
  }
  return os << "}";
}

template <typename T> ostream &operator<<(ostream &os, const set<T> &v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << *it;
  }
  return os << "]";
}

template <typename F, typename S>
ostream &operator<<(ostream &os, const map<F, S> &v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}

#define dbg(args...)                                                           \
  do {                                                                         \
    cerr << #args << " : ";                                                    \
    faltu(args);                                                               \
  } while (0)

clock_t tStart = clock();
#define timeStamp                                                              \
  dbg("Execution Time: ", (double)(clock() - tStart) / CLOCKS_PER_SEC)

void faltu() { cerr << endl; }

template <typename T> void faltu(T a[], int n) {
  for (int i = 0; i < n; ++i)
    cerr << a[i] << ' ';
  cerr << endl;
}

template <typename T, typename... hello>
void faltu(T arg, const hello &...rest) {
  cerr << arg << ' ';
  faltu(rest...);
}
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    new_data_set;

/**___________________________________________________**/

int main() {
  FASTIO
  ///*
  // #ifndef ONLINE_JUDGE
  // 	freopen("in.txt", "r", stdin);
  // 	freopen("out.txt", "w", stdout);
  // 	freopen("error.txt", "w", stderr);
  // #endif
  //*/
  int T;
  // scanf("%d", &T);
  T = 1;
  for (int cs = 1; cs <= T; cs++) {
    int n;
    cin >> n;
    vector<int> a(n + 10), b(n + 10);
    for (int i = 0; i <= n; i++)
      b[i] = 1e9;
    for (int i = 0; i < n - 1; i++)
      cin >> a[i]; //, --a[i];

    for (int i = 0; i < n - 1; i++) {
      for (int j = i; j <= i + 1 && j + 1 < n; j++) {
        // dbg(i, b[j], a[i]);
        b[j] = min(b[j], a[i]);
        // dbg(i, b[j], a[i]);
      }
      // cerr << "--------------\n";
    }
    b[n - 1] = a[n - 2];
    int ans = 0;
    for (int i = 0; i < n; i++) {
      // dbg(b[i]);
      ans += b[i];
    }
    cout << ans << endl;
  }
  return 0;
}