Problem p02626 (C++) — buggy submission, verdict: Runtime Error

#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
// #pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#define __builtin_popcountll __popcnt64
#endif

#include <limits.h>
#include <math.h>
#include <time.h>

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
#define int long long
// #define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v)                                                         \\
  REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\\n" : " ")
template <typename T1, typename T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <typename T1, typename T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 1e9 + 7;
constexpr int MAX = 500050;
const double pi = acos(-1);
constexpr double EPS = 1e-8;
constexpr ll LINF = 1e18 + 1;
constexpr int INF = 1e18 + 1;

int f(int x, int y, int z) {
  if (x == 0 && y == 0 && z == 0)
    return 0;
  if (((x & 1) ^ (y & 1)) == (z & 1)) {
    int res1 = 2 * f(x >> 1, y >> 1, z >> 1);
    int res2 = INF;
    if (x > 0)
      res2 = 1 + 2 * f((x - 1) >> 1, (y + 1) >> 1, z >> 1);
    int res = min(res1, res2);
    if (res >= INF)
      return INF;
    else
      return res;
  } else {
    return INF;
  }
}

void solve() {
  int N;
  cin >> N;
  vector<int> A(N);
  REP(i, N) { cin >> A[i]; }
  int x = A[0], y = A[1];
  int z = 0;
  FOR(i, 2, N) z ^= A[i];
  ll ans = f(x, y, z);
  if (ans >= INF || ans == x)
    print(-1);
  else
    print(ans);
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  // while (test());
  // int q;
  // cin >> q;
  // while (q--)
  solve();
}


Error: 1

Fixed submission:

#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
// #pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#define __builtin_popcountll __popcnt64
#endif

#include <limits.h>
#include <math.h>
#include <time.h>

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
#define int long long
// #define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v)                                                         \\
  REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\\n" : " ")
template <typename T1, typename T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <typename T1, typename T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 1e9 + 7;
constexpr int MAX = 500050;
const double pi = acos(-1);
constexpr double EPS = 1e-8;
constexpr ll LINF = 1e18 + 1;
constexpr int INF = 1e9 + 1;

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 (k == 0)
    return 1;
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
ll add(ll x, ll y) {
  x += y;
  if (x >= MOD)
    return x - MOD;
  return x;
}
ll sub(ll x, ll y) {
  x -= y;
  if (x < 0)
    return x + MOD;
  return x;
}
ll mult(ll x, ll y) { return (x * y) % MOD; }
ll bin_pow(ll x, ll p) {
  if (p == 0)
    return 1;
  if (p & 1)
    return mult(x, bin_pow(x, p - 1));
  return bin_pow(mult(x, x), p / 2);
}
const int mod = 1000000007;
// const int mod = 998244353;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
void fail() {
  print(-1);
  exit(0);
}

void solve() {
  int N;
  cin >> N;
  vector<int> A(N);
  REP(i, N) { cin >> A[i]; }
  int x = A[0], y = A[1];
  int z = 0;
  int x0 = x, y0 = y;
  FOR(i, 2, N) z ^= A[i];
  int ans = 0;
  REPR(j, 60) {
    if (z & (1LL << j)) {
      if ((!(x & 1LL << j)) && !(y & 1LL << j)) {
        int r = 0;
        REP(k, j) if (y & (1LL << k)) r |= (1LL << k);
        int need = (1LL << j) - r;
        if (x < need)
          fail();
        ans += need;
        x -= need;
        y += need;
      } else if ((x & 1LL << j) && (y & 1LL << j)) {
        int need = 1;
        REP(k, j) if (x & (1LL << k)) need += (1LL << k);
        ans += need;
        x -= need;
        y += need;
      }
    } else {
      if ((x & (1LL << j)) && (!(y & 1LL << j))) {
        // xのjビット目を下ろす
        int need1 = 1;
        REP(k, j) if (x & (1LL << k)) need1 += (1LL << k);

        // yのjビット目を立てる
        int r = 0;
        REP(k, j) if (y & (1LL << k)) r |= (1LL << k);
        int need2 = (1LL << j) - r;

        int need = min(need1, need2);
        x -= need;
        y += need;
        ans += need;
      } else if ((!(x & 1LL << j)) && (y & 1LL << j)) {
        fail();
      }
    }
  }
  if (x == 0)
    fail();
  if ((x ^ y) == z)
    exit(1);
  else {
    print(-1);
  }
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  // int q;
  // cin >> q;
  // while (q--)
  solve();
}