Problem p03611 (C++)

Buggy submission (status: Runtime Error):
/////////////////////////////////////////////////
/////             Give me AC!!!!            /////
/////////////////////////////////////////////////
// ↑これじゃ気合いが足りない！
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/////
///お願いしますACをくださいそうじゃないと僕泣きますお願いしますACをくださいJudge様....
////////
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define rep(i, N) for (int i = 0; i < (N); i++)
#define erep(i, N) for (int i = N - 1; i >= 0; i--)
const int MOD = 1000000007;
const int MAX = 510000;
const ld PI = (acos(-1));
using Graph = vector<vector<int>>;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
typedef pair<int, int> P;
typedef pair<ll, ll> PLL;
ld rad(ld a) { return a * 180 / PI; }
const int dx[4] = {1, 0, -1, 0}; // 2次元グリッド上のx軸方向
const int dy[4] = {0, 1, 0, -1}; // 2次元グリッド上のy軸方向

/*template<int MOD> struct Fp {
    ll val;
    constexpr Fp(ll v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) +=
r; } constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -=
r; } constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *=
r; } constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /=
r; } constexpr Fp& operator += (const Fp& r) noexcept { val += r.val; if (val >=
MOD) val -= MOD; return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        ll a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            ll t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x)
noexcept { return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, ll n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
using mint = Fp<MOD>;*/
struct UnionFind {
  vector<int> par;

  UnionFind(int n) : par(n, -1) {}

  int root(int x) {
    if (par[x] < 0)
      return x;
    else
      return par[x] = root(par[x]);
  }

  bool same(int x, int y) { return root(x) == root(y); }

  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      swap(x, y); // merge technique
    par[x] += par[y];
    par[y] = x;
    return true;
  }

  int size(int x) { return -par[root(x)]; }
};

vector<pair<ll, ll>> prime_factorize(ll N) {
  vector<pair<ll, ll>> res;
  for (ll a = 2; a * a <= N; ++a) {
    if (N % a != 0)
      continue;
    ll ex = 0; // 指数

    // 割れる限り割り続ける
    while (N % a == 0) {
      ++ex;
      N /= a;
    }

    // その結果を push
    res.push_back({a, ex});
  }

  // 最後に残った数について
  if (N != 1)
    res.push_back({N, 1});
  return res;
}

// dpTable
vector<ll> dp(1000000, 100000000000);

ll modpow(ll a, ll n, ll mod) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

ll mod(ll val, ll m) {
  ll res = val % m;
  if (res < 0)
    res += m;
  return res;
}

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}

// 二項係数計算
long long COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

int main() {
  int N;
  cin >> N;
  vector<int> X(100001, 0);
  rep(i, N) {
    int A;
    cin >> A;
    if (A != 0) {
      X.at(i - 1)++;
    }
    X.at(i)++;
    X.at(i + 1)++;
  }
  sort(X.begin(), X.end());
  reverse(X.begin(), X.end());
  cout << X.at(0) << endl;
  return 0;
}

Fixed submission:
/////////////////////////////////////////////////
/////             Give me AC!!!!            /////
/////////////////////////////////////////////////
// ↑これじゃ気合いが足りない！
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/////
///お願いしますACをくださいそうじゃないと僕泣きますお願いしますACをくださいJudge様....
////////
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define rep(i, N) for (int i = 0; i < (N); i++)
#define erep(i, N) for (int i = N - 1; i >= 0; i--)
const int MOD = 1000000007;
const int MAX = 510000;
const ld PI = (acos(-1));
using Graph = vector<vector<int>>;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
typedef pair<int, int> P;
typedef pair<ll, ll> PLL;
ld rad(ld a) { return a * 180 / PI; }
const int dx[4] = {1, 0, -1, 0}; // 2次元グリッド上のx軸方向
const int dy[4] = {0, 1, 0, -1}; // 2次元グリッド上のy軸方向

/*template<int MOD> struct Fp {
    ll val;
    constexpr Fp(ll v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) +=
r; } constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -=
r; } constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *=
r; } constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /=
r; } constexpr Fp& operator += (const Fp& r) noexcept { val += r.val; if (val >=
MOD) val -= MOD; return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        ll a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            ll t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x)
noexcept { return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, ll n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
using mint = Fp<MOD>;*/
struct UnionFind {
  vector<int> par;

  UnionFind(int n) : par(n, -1) {}

  int root(int x) {
    if (par[x] < 0)
      return x;
    else
      return par[x] = root(par[x]);
  }

  bool same(int x, int y) { return root(x) == root(y); }

  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      swap(x, y); // merge technique
    par[x] += par[y];
    par[y] = x;
    return true;
  }

  int size(int x) { return -par[root(x)]; }
};

vector<pair<ll, ll>> prime_factorize(ll N) {
  vector<pair<ll, ll>> res;
  for (ll a = 2; a * a <= N; ++a) {
    if (N % a != 0)
      continue;
    ll ex = 0; // 指数

    // 割れる限り割り続ける
    while (N % a == 0) {
      ++ex;
      N /= a;
    }

    // その結果を push
    res.push_back({a, ex});
  }

  // 最後に残った数について
  if (N != 1)
    res.push_back({N, 1});
  return res;
}

// dpTable
vector<ll> dp(1000000, 100000000000);

ll modpow(ll a, ll n, ll mod) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

ll mod(ll val, ll m) {
  ll res = val % m;
  if (res < 0)
    res += m;
  return res;
}

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}

// 二項係数計算
long long COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

int main() {
  int N;
  cin >> N;
  vector<int> X(100001, 0);
  rep(i, N) {
    int A;
    cin >> A;
    if (A != 0) {
      X.at(A - 1)++;
    }
    X.at(A)++;
    X.at(A + 1)++;
  }
  sort(X.begin(), X.end());
  reverse(X.begin(), X.end());
  cout << X.at(0) << endl;
  return 0;
}