Problem p03954 (C++)

Buggy submission (status: Runtime Error):
/* be name khoda */

// #define stream_enable
// #define long_enable
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <vector>
using namespace std;

#ifdef stream_enable
#define cin sss
#endif
#ifdef long_enable
typedef long long int ll;
#else
typedef int ll;
#endif

typedef pair<ll, ll> pii;
typedef pair<pii, ll> ppi;
typedef pair<ll, pii> pip;
typedef vector<ll> vi;
typedef vector<pii> vpii;

const ll MOD = 1000000007;
const long long BIG = 1446803456761533460;
const int Big = 336860180;

#define F first
#define S second
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()

#define debug(x) cout << #x << " -> " << (x) << endl
#define debug2(x, y)                                                           \
  cout << #x << ' ' << #y << " -> " << (x) << ' ' << (y) << endl
#define debug3(x, y, z)                                                        \
  cout << #x << ' ' << #y << ' ' << #z << " -> " << (x) << ' ' << (y) << ' '   \
       << (z) << endl
#define debug4(x, y, z, t)                                                     \
  cout << #x << ' ' << #y << ' ' << #z << ' ' << #t << " -> " << (x) << ' '    \
       << (y) << ' ' << (z) << ' ' << (t) << endl
#define debugp(x)                                                              \
  cout << #x << " -> "                                                         \
       << "(" << (x).F << ", " << (x).S << ")" << endl
#define debuga(x, n)                                                           \
  cout << #x << " -> ";                                                        \
  fori(i1_da, n) { cout << (x)[i1_da] << ' '; }                                \
  cout << endl
#define debugap(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dap, n) {                                                            \
    cout << "(" << (x)[i1_dap].F << ", " << (x)[i1_dap].S << ")\n";            \
  }                                                                            \
  cout << endl
#define debugaa(x, n, m)                                                       \
  cout << #x << " ->\n";                                                       \
  fori(i1_daa, n) {                                                            \
    fori(i2_daa, m) { cout << (x)[i1_daa][i2_daa] << ' '; }                    \
    cout << '\n';                                                              \
  }                                                                            \
  cout << endl
#define debugav(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dav, n) {                                                            \
    fori(i2_dav, (x)[i1_dav].size()) { cout << (x)[i1_dav][i2_dav] << ' '; }   \
    cout << '\n';                                                              \
  }                                                                            \
  cout << endl
#define debugia(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dia, n) { cout << i1_dia << " : " << (x)[i1_dia] << '\n'; }          \
  cout << endl

#define forifrom(i, s, n) for (ll i = (s); i < (n); ++i)
#define forirto(i, n, e) for (ll i = (n)-1; i >= (e); --i)
#define fori(i, n) forifrom(i, 0, n)
#define forir(i, n) forirto(i, n, 0)

#define smin(a, b) a = min(a, (b))
#define smax(a, b) a = max(a, (b))

#define Add(a, b) a = (a + (b)) % MOD
#define Mul(a, b) a = (a * (b)) % MOD

stringstream sss;

// -----------------------------------------------------------------------

const ll maxn = 100010;

ll n, ar[maxn];

void MAIN() {

  cin >> n;
  fori(i, n * 2 - 1) cin >> ar[i];
  ll l = 1, r = n * 2;
  while (r - l > 1) {
    ll m = (l + r) / 2;
    ll zer = n, one = n;
    fori(i, n - 1) {
      if (ar[i] >= m && ar[i + 1] >= m) {
        smin(one, n - 2 - i);
      } else if (ar[i] < m && ar[i + 1] < m) {
        smin(zer, n - 2 - i);
      }
    }
    forifrom(i, n - 1, n * 2 - 2) {
      if (ar[i] >= m && ar[i + 1] >= m) {
        smin(one, i - n + 1);
      } else if (ar[i] < m && ar[i + 1] < m) {
        smin(zer, i - n + 1);
      }
    }
    if (one < zer || zer == one && (ar[n - 1] >= m) ^ (n & 1 ^ 1)) {
      l = m;
    } else {
      r = m;
    }
  }
  cout << l << '\n';
}

// -----------------------------------------------------------------------

int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cout << fixed << setprecision(10);
  sss << R"(
4
1 6 3 7 4 5 2
    )";
  MAIN();
  return 0;
}


Fixed submission:
/* be name khoda */

// #define stream_enable
// #define long_enable
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <vector>
using namespace std;

#ifdef stream_enable
#define cin sss
#endif
#ifdef long_enable
typedef long long int ll;
#else
typedef int ll;
#endif

typedef pair<ll, ll> pii;
typedef pair<pii, ll> ppi;
typedef pair<ll, pii> pip;
typedef vector<ll> vi;
typedef vector<pii> vpii;

const ll MOD = 1000000007;
const long long BIG = 1446803456761533460;
const int Big = 336860180;

#define F first
#define S second
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()

#define debug(x) cout << #x << " -> " << (x) << endl
#define debug2(x, y)                                                           \
  cout << #x << ' ' << #y << " -> " << (x) << ' ' << (y) << endl
#define debug3(x, y, z)                                                        \
  cout << #x << ' ' << #y << ' ' << #z << " -> " << (x) << ' ' << (y) << ' '   \
       << (z) << endl
#define debug4(x, y, z, t)                                                     \
  cout << #x << ' ' << #y << ' ' << #z << ' ' << #t << " -> " << (x) << ' '    \
       << (y) << ' ' << (z) << ' ' << (t) << endl
#define debugp(x)                                                              \
  cout << #x << " -> "                                                         \
       << "(" << (x).F << ", " << (x).S << ")" << endl
#define debuga(x, n)                                                           \
  cout << #x << " -> ";                                                        \
  fori(i1_da, n) { cout << (x)[i1_da] << ' '; }                                \
  cout << endl
#define debugap(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dap, n) {                                                            \
    cout << "(" << (x)[i1_dap].F << ", " << (x)[i1_dap].S << ")\n";            \
  }                                                                            \
  cout << endl
#define debugaa(x, n, m)                                                       \
  cout << #x << " ->\n";                                                       \
  fori(i1_daa, n) {                                                            \
    fori(i2_daa, m) { cout << (x)[i1_daa][i2_daa] << ' '; }                    \
    cout << '\n';                                                              \
  }                                                                            \
  cout << endl
#define debugav(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dav, n) {                                                            \
    fori(i2_dav, (x)[i1_dav].size()) { cout << (x)[i1_dav][i2_dav] << ' '; }   \
    cout << '\n';                                                              \
  }                                                                            \
  cout << endl
#define debugia(x, n)                                                          \
  cout << #x << " ->\n";                                                       \
  fori(i1_dia, n) { cout << i1_dia << " : " << (x)[i1_dia] << '\n'; }          \
  cout << endl

#define forifrom(i, s, n) for (ll i = (s); i < (n); ++i)
#define forirto(i, n, e) for (ll i = (n)-1; i >= (e); --i)
#define fori(i, n) forifrom(i, 0, n)
#define forir(i, n) forirto(i, n, 0)

#define smin(a, b) a = min(a, (b))
#define smax(a, b) a = max(a, (b))

#define Add(a, b) a = (a + (b)) % MOD
#define Mul(a, b) a = (a * (b)) % MOD

stringstream sss;

// -----------------------------------------------------------------------

const ll maxn = 200010;

ll n, ar[maxn];

void MAIN() {

  cin >> n;
  fori(i, n * 2 - 1) cin >> ar[i];
  ll l = 1, r = n * 2;
  while (r - l > 1) {
    ll m = (l + r) / 2;
    ll zer = n, one = n;
    fori(i, n - 1) {
      if (ar[i] >= m && ar[i + 1] >= m) {
        smin(one, n - 2 - i);
      } else if (ar[i] < m && ar[i + 1] < m) {
        smin(zer, n - 2 - i);
      }
    }
    forifrom(i, n - 1, n * 2 - 2) {
      if (ar[i] >= m && ar[i + 1] >= m) {
        smin(one, i - n + 1);
      } else if (ar[i] < m && ar[i + 1] < m) {
        smin(zer, i - n + 1);
      }
    }
    if (one < zer || zer == one && (ar[n - 1] >= m) ^ (n & 1 ^ 1)) {
      l = m;
    } else {
      r = m;
    }
  }
  cout << l << '\n';
}

// -----------------------------------------------------------------------

int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cout << fixed << setprecision(10);
  sss << R"(
4
1 6 3 7 4 5 2
    )";
  MAIN();
  return 0;
}