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

#include <bits/stdc++.h>

using namespace std;

using ll = int64_t;
// using ll = long long;
using ull = uint64_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
using f64 = double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using ld = double;

#define X first
#define Y second

#ifndef ONLINE_JUDGE
#define FWRITE
#endif

namespace io {

#ifndef FWRITE
#include <unistd.h>
auto unistd_read = read;
auto unistd_write = write;
#endif
const int BUFSIZE = 1 << 20;

int isize, osize;
char ibuf[BUFSIZE + 10], obuf[BUFSIZE + 10];
char *is, *it, *os = obuf, *ot = obuf + BUFSIZE;

char getchar() {
  if (is == it) {
    is = ibuf;
#ifdef FWRITE
    it = ibuf + fread(ibuf, 1, BUFSIZE, stdin);
#else
    it = ibuf + unistd_read(STDIN_FILENO, ibuf, BUFSIZE);
#endif
    if (is == it)
      return EOF;
  }
  return *is++;
}

char getalpha() {
  char c = getchar();
  while (!isalpha(c))
    c = getchar();
  return c;
}

void putchar(char c) {
  *os++ = c;
  if (os == ot) {
#ifdef FWRITE
    fwrite(obuf, 1, BUFSIZE, stdout);
#else
    unistd_write(STDOUT_FILENO, obuf, BUFSIZE);
#endif
    os = obuf;
  }
}

int inp() {
  int x = 0, f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return -1;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  return f ? -x : x;
}

ll inp_ll() {
  ll x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar())
    if (ch == '-')
      f = 1;
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  return f ? -x : x;
}

template <class T> bool read(T &x) {
  x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return 0;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  if (f)
    x = -x;
  return 1;
}

bool read(char *s) {
  char *t = s;
  char ch = getchar();
  for (; ch == ' ' || ch == '\\n'; ch = getchar())
    ;
  for (; ch != ' ' && ch != '\\n' && ch != EOF; ch = getchar())
    *t++ = ch;
  *t = 0;
  return s != t;
}

template <class T, class... Args> bool read(T &x, Args &...args) {
  return read(x) && read(args...);
}

template <class T> bool readln(T &x) {
  x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return 0;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  if (f)
    x = -x;
  for (; ch != '\\n' && ch != EOF; ch = getchar())
    ;
  return 1;
}

bool readln(char *s) {
  char *t = s;
  while (1) {
    char ch = getchar();
    if (ch == '\\n' || ch == EOF)
      break;
    *t++ = ch;
  }
  *t = 0;
  return s != t;
}

template <class T, class... Args> bool readln(T &x, Args &...args) {
  return read(x) && readln(args...);
}

template <class T> void write(T x) {
  static char s[22];
  static char *it = s + 20;
  static char *end = s + 20;

  if (x < 0) {
    putchar('-');
    x = -x;
  }

  do {
    *--it = x % 10 + '0';
    x /= 10;
  } while (x);
  /*
  if (!x)
          *-- it = '0';
  while (x)
  {
          *-- it = x%10+'0';
          x /= 10;
  }
  */
  for (; it < end; ++it)
    putchar(*it);
}

void write(const char *s) {
  for (; *s; ++s)
    putchar(*s);
}

template <> void write(char *s) { write((const char *)s); }

template <> void write(char c) { putchar(c); }

template <class T, class... Args> void write(T x, Args... args) {
  write(x);
  write(args...);
}

void writeln() { putchar('\\n'); }

template <class T, class... Args> void writeln(T x, Args... args) {
  write(x);
  writeln(args...);
}

template <class Iterator> bool input(Iterator st, Iterator ed) {
  for (; st != ed; ++st) {
    if (!read(*st))
      return false;
  }
  return true;
}

template <class T> bool input(T &a) { return input(a.begin(), a.end()); }

template <class Iterator>
void print(Iterator st, Iterator ed, const char *c = " ") {
  int flag = 0;
  for (; st != ed; ++st) {
    if (flag)
      write(c);
    flag = 1;
    write(*st);
  }
  writeln();
}

template <class T> void print(const T &a, const char *c = " ") {
  print(a.begin(), a.end(), c);
}

struct ender {
  ~ender() {
    if (os != obuf)
#ifdef FWRITE
      fwrite(obuf, 1, os - obuf, stdout);
#else
      unistd_write(STDOUT_FILENO, obuf, os - obuf);
#endif
  }
} __ender;

} // namespace io

int64_t power(int64_t a, int64_t b, int64_t p) {
  if (!b)
    return 1;
  int64_t t = power(a, b >> 1, p);
  t = t * t % p;
  if (b & 1)
    t = t * a % p;
  return t;
}

// mt19937_64 rd(chrono::steady_clock::now().time_since_epoch().count());
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
// mt19937 rd(1);

using namespace io;

template <class T> inline void freshmin(T &a, const T &b) {
  if (a > b)
    a = b;
}

template <class T> inline void freshmax(T &a, const T &b) {
  if (a < b)
    a = b;
}

// const ll B = 31;
// const ll MOD = 998244353;
const int INF = 1000000010;
const ll INFll = 4000000000000000000LL;
const int MAXN = 1 << 21 | 10;

int dx[] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[] = {0, 0, -1, 1, -1, 1, -1, 1};

ld det(ld x1, ld y1, ld x2, ld y2, ld x3, ld y3) {
  return x1 * y2 - x2 * y1 + x2 * y3 - x3 * y2 + x3 * y1 - x1 * y3;
}

int n;
ll a[MAXN];
const int K = 20;

vector<ll> v[MAXN];

void solve() {
  /*
  read(n);
  input(a + 1, a + n + 1);
  ll d = 0;
  for (int i = 3; i <= n; ++i) d ^= a[i];

  int d1 = d >> K;
  int d2 = d & ((1LL << K) - 1);
  for (int x2 = 0; x2 < 1LL << K; ++x2)
  {
          int y2 = x2 ^ d2;
          v[x2 + y2].push_back(x2);
  }
  for (int i = 0; i < 1LL << (K + 1); ++i)
  {
          sort(v[i].begin(), v[i].end());
  }

  ll res = 0;
  for (int x1 = 0; x1 < 1LL << K; ++x1)
  {
          int y1 = x1 ^ d1;
          ll high = ll(x1 + y1) << K;
          if (high > a[1] + a[2]) continue;
          ll low = a[1] + a[2] - high;

          //if (!(0 <= low && low < 1LL << (K + 1))) continue;
          ll bound = a[1] - (ll(x1) << K);
          //freshmin(bound, 1LL << K);
          auto it = upper_bound(v[low].begin(), v[low].end(), int(bound));
          if (it != v[low].begin())
          {
                  --it;
                  freshmax(res, ll(x1) << K | *it);
          }
  }

  if (res <= 0) return writeln(-1);
  res = a[1] - res;
  writeln(res);
  */
  read(n);
  input(a + 1, a + n + 1);
  ll d = 0;
  for (int i = 3; i <= n; ++i)
    d ^= a[i];

  int d1 = d >> K;
  int d2 = d & ((1LL << K) - 1);
  for (int x2 = 0; x2 < 1LL << K; ++x2) {
    int y2 = x2 ^ d2;
    v[x2 + y2].push_back(x2);
  }
  for (int i = 0; i < 1LL << (K + 1); ++i) {
    sort(v[i].begin(), v[i].end());
  }

  ll res = 0;
  for (int x1 = 0; x1 < 1LL << K; ++x1) {
    int y1 = x1 ^ d1;
    ll high = ll(x1 + y1) << K;
    if (high > a[1] + a[2])
      continue;
    ll low = a[1] + a[2] - high;
    if (!(0 <= low && low < 1LL << (K + 1)))
      continue;

    ll bound = a[1] - (ll(x1) << K);
    auto it = upper_bound(v[low].begin(), v[low].end(), bound);
    if (it != v[low].begin()) {
      --it;
      freshmax(res, ll(x1) << K | *it);
    }
  }

  if (res <= 0)
    return writeln(-1);
  res = a[1] - res;
  writeln(res);
}

int main() {

  int T = 1;
  // read(T);
  for (int test = 1; test <= T; ++test) {
    // write("Case #", test, ": ");
    solve();
  }

  return 0;
}

Error: -6
terminate called after throwing an instance of 'St9bad_alloc'
  what():  std::bad_alloc


Fixed submission:

#include <bits/stdc++.h>

using namespace std;

using ll = int64_t;
// using ll = long long;
using ull = uint64_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
using f64 = double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using ld = double;

#define X first
#define Y second

#ifndef ONLINE_JUDGE
#define FWRITE
#endif

namespace io {

#ifndef FWRITE
#include <unistd.h>
auto unistd_read = read;
auto unistd_write = write;
#endif
const int BUFSIZE = 1 << 20;

int isize, osize;
char ibuf[BUFSIZE + 10], obuf[BUFSIZE + 10];
char *is, *it, *os = obuf, *ot = obuf + BUFSIZE;

char getchar() {
  if (is == it) {
    is = ibuf;
#ifdef FWRITE
    it = ibuf + fread(ibuf, 1, BUFSIZE, stdin);
#else
    it = ibuf + unistd_read(STDIN_FILENO, ibuf, BUFSIZE);
#endif
    if (is == it)
      return EOF;
  }
  return *is++;
}

char getalpha() {
  char c = getchar();
  while (!isalpha(c))
    c = getchar();
  return c;
}

void putchar(char c) {
  *os++ = c;
  if (os == ot) {
#ifdef FWRITE
    fwrite(obuf, 1, BUFSIZE, stdout);
#else
    unistd_write(STDOUT_FILENO, obuf, BUFSIZE);
#endif
    os = obuf;
  }
}

int inp() {
  int x = 0, f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return -1;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  return f ? -x : x;
}

ll inp_ll() {
  ll x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar())
    if (ch == '-')
      f = 1;
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  return f ? -x : x;
}

template <class T> bool read(T &x) {
  x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return 0;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  if (f)
    x = -x;
  return 1;
}

bool read(char *s) {
  char *t = s;
  char ch = getchar();
  for (; ch == ' ' || ch == '\\n'; ch = getchar())
    ;
  for (; ch != ' ' && ch != '\\n' && ch != EOF; ch = getchar())
    *t++ = ch;
  *t = 0;
  return s != t;
}

template <class T, class... Args> bool read(T &x, Args &...args) {
  return read(x) && read(args...);
}

template <class T> bool readln(T &x) {
  x = 0;
  int f = 0;
  char ch;
  for (ch = getchar(); !isdigit(ch); ch = getchar()) {
    if (ch == EOF)
      return 0;
    if (ch == '-')
      f = 1;
  }
  for (; isdigit(ch); x = x * 10 + ch - '0', ch = getchar())
    ;
  if (f)
    x = -x;
  for (; ch != '\\n' && ch != EOF; ch = getchar())
    ;
  return 1;
}

bool readln(char *s) {
  char *t = s;
  while (1) {
    char ch = getchar();
    if (ch == '\\n' || ch == EOF)
      break;
    *t++ = ch;
  }
  *t = 0;
  return s != t;
}

template <class T, class... Args> bool readln(T &x, Args &...args) {
  return read(x) && readln(args...);
}

template <class T> void write(T x) {
  static char s[22];
  static char *it = s + 20;
  static char *end = s + 20;

  if (x < 0) {
    putchar('-');
    x = -x;
  }

  do {
    *--it = x % 10 + '0';
    x /= 10;
  } while (x);
  /*
  if (!x)
          *-- it = '0';
  while (x)
  {
          *-- it = x%10+'0';
          x /= 10;
  }
  */
  for (; it < end; ++it)
    putchar(*it);
}

void write(const char *s) {
  for (; *s; ++s)
    putchar(*s);
}

template <> void write(char *s) { write((const char *)s); }

template <> void write(char c) { putchar(c); }

template <class T, class... Args> void write(T x, Args... args) {
  write(x);
  write(args...);
}

void writeln() { putchar('\\n'); }

template <class T, class... Args> void writeln(T x, Args... args) {
  write(x);
  writeln(args...);
}

template <class Iterator> bool input(Iterator st, Iterator ed) {
  for (; st != ed; ++st) {
    if (!read(*st))
      return false;
  }
  return true;
}

template <class T> bool input(T &a) { return input(a.begin(), a.end()); }

template <class Iterator>
void print(Iterator st, Iterator ed, const char *c = " ") {
  int flag = 0;
  for (; st != ed; ++st) {
    if (flag)
      write(c);
    flag = 1;
    write(*st);
  }
  writeln();
}

template <class T> void print(const T &a, const char *c = " ") {
  print(a.begin(), a.end(), c);
}

struct ender {
  ~ender() {
    if (os != obuf)
#ifdef FWRITE
      fwrite(obuf, 1, os - obuf, stdout);
#else
      unistd_write(STDOUT_FILENO, obuf, os - obuf);
#endif
  }
} __ender;

} // namespace io

int64_t power(int64_t a, int64_t b, int64_t p) {
  if (!b)
    return 1;
  int64_t t = power(a, b >> 1, p);
  t = t * t % p;
  if (b & 1)
    t = t * a % p;
  return t;
}

// mt19937_64 rd(chrono::steady_clock::now().time_since_epoch().count());
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
// mt19937 rd(1);

using namespace io;

template <class T> inline void freshmin(T &a, const T &b) {
  if (a > b)
    a = b;
}

template <class T> inline void freshmax(T &a, const T &b) {
  if (a < b)
    a = b;
}

// const ll B = 31;
// const ll MOD = 998244353;
const int INF = 1000000010;
const ll INFll = 4000000000000000000LL;
const int MAXN = 1 << 21 | 10;

int dx[] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[] = {0, 0, -1, 1, -1, 1, -1, 1};

ld det(ld x1, ld y1, ld x2, ld y2, ld x3, ld y3) {
  return x1 * y2 - x2 * y1 + x2 * y3 - x3 * y2 + x3 * y1 - x1 * y3;
}

int n;
ll a[MAXN];
const int K = 20;

vector<int> v[MAXN];

void solve() {
  read(n);
  input(a + 1, a + n + 1);
  ll d = 0;
  for (int i = 3; i <= n; ++i)
    d ^= a[i];

  int d1 = d >> K;
  int d2 = d & ((1LL << K) - 1);
  for (int x2 = 0; x2 < 1LL << K; ++x2) {
    int y2 = x2 ^ d2;
    v[x2 + y2].push_back(x2);
  }
  for (int i = 0; i < 1LL << (K + 1); ++i) {
    sort(v[i].begin(), v[i].end());
  }

  ll res = 0;
  for (int x1 = 0; x1 < 1LL << K; ++x1) {
    int y1 = x1 ^ d1;
    ll high = ll(x1 + y1) << K;
    if (high > a[1] + a[2])
      continue;
    ll low = a[1] + a[2] - high;

    ll bound = a[1] - (ll(x1) << K);
    auto it = upper_bound(v[low].begin(), v[low].end(), bound);
    if (it != v[low].begin()) {
      --it;
      freshmax(res, ll(x1) << K | *it);
    }
  }

  if (res <= 0)
    return writeln(-1);
  res = a[1] - res;
  writeln(res);
}

int main() {

  int T = 1;
  // read(T);
  for (int test = 1; test <= T; ++test) {
    // write("Case #", test, ": ");
    solve();
  }

  return 0;
}