Problem p02626 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

#define rep(i, n) for (lint i = 0; i < n; i++)
#define repr(i, n) for (lint i = n - 1; i >= 0; i--)
#define repi(i, ini, n) for (lint i = ini; i < n; i++)
#define repir(i, ini, n) for (lint i = n - 1; i >= ini; i--)
#define repb(i, start, end) for (lint i = start; i <= end; i++)
#define repbr(i, start, end) for (lint i = end; i >= start; i--)

#define bit(n) (1LL << (n))

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rg(v, ini, end) v.begin() + ini, v.begin() + end
#define rrg(v, ini, end) v.rbegin() + ini, v.rbegin() + end

#define ret return 0;
#define chmax(a, b) a = mmax(a, b);

namespace {

using lint = long long;
using ulint = unsigned long long;
using ld = long double;
struct xy {
  lint x, y;
  xy() : x(0), y(0) {}
  xy(lint _x, lint _y) : x(_x), y(_y) {}
  xy operator+(const xy &p) const { return xy(x + p.x, y + p.y); }
  bool operator<(xy p) const {
    if (y == p.y)
      return x < p.x;
    return y < p.y;
  }
};
struct xyd {
  ld x, y;
  xyd() : x(0), y(0) {}
  xyd(long double _x, long double _y) : x(_x), y(_y) {}
};
using vec = vector<lint>;
using vecd = vector<ld>;
using vecs = vector<string>;
using vecp = vector<xy>;
template <class T> using vect = vector<T>;
class vec2 : public vector<vector<lint>> {
public:
  vec2() {}
  vec2(lint n) : vector(n) {}
  vec2(lint h, lint w) : vector(h, vector<lint>(w)) {}
  vec2(lint h, lint w, lint v) : vector(h, vector<lint>(w, v)) {}
};

template <class T> using priq = priority_queue<T>;
template <class T> using rpriq = priority_queue<T, vector<T>, greater<T>>;
template <class Key, class Val> using hashmap = unordered_map<Key, Val>;
template <class Key> using hashset = unordered_set<Key>;

mt19937 mtrand((random_device())());

const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;

template <class T> constexpr auto msum(T arg0) { return arg0; }

template <class T, class... Types> constexpr auto msum(T arg0, Types... args) {
  static_assert(sizeof...(args) > 0, "arg err");

  return arg0 + msum(args...);
}

template <class It> constexpr typename It::value_type mmax(It begin, It end) {
  return *max_element(begin, end);
}

template <class It> constexpr typename It::value_type mmin(It begin, It end) {
  return *min_element(begin, end);
}

template <class T> constexpr auto mmax(T arg) { return arg; }

template <class T, class... Types> constexpr auto mmax(T arg0, Types... args) {
  using promote_t = decltype(msum(arg0, args...));

  return max(static_cast<promote_t>(arg0),
             static_cast<promote_t>(mmax(args...)));
}

template <class T> constexpr auto mmin(T arg) { return arg; }

template <class T, class... Types> constexpr auto mmin(T arg0, Types... args) {
  using promote_t = decltype(msum(arg0, args...));

  return min(static_cast<promote_t>(arg0),
             static_cast<promote_t>(mmin(args...)));
}

template <class T> struct Mplus {
  T operator()(const T &a, const T &b) { return a + b; }

  const static T id = T(0);
};

template <class It, class T = typename It::value_type, class Monoid = Mplus<T>>
T acc(It begin, It end, Monoid f = Mplus<T>()) {
  return accumulate(begin, end, Monoid::id, f);
}

constexpr auto clamp(lint val, lint left, lint right) {
  return mmax(mmin(val, right), left);
}

constexpr lint div2(lint p, lint q) { return (p + q - 1) / q; }

#if (__cplusplus < 201703L)

lint gcd(lint a, lint b) {
  while (1) {
    if (a < b)
      swap(a, b);
    if (!b)
      break;
    a %= b;
  }
  return a;
}

lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }

#endif

constexpr lint powInt(lint a, lint b) {
  if (b == 0) {
    return 1;
  }
  if (b == 1) {
    return a;
  }
  lint tmp = powInt(a, b / 2);
  return (b % 2 == 1 ? a * tmp * tmp : tmp * tmp);
}

template <class T> T sgn(T val) {
  if (val == T(0))
    return T(0);
  if (val < 0)
    return T(-1);
  if (val > 0)
    return T(1);
}

template <class T> constexpr auto modK_belowN(T k, T MOD, T n) {
  return (n + MOD - k - 1) / MOD;
}

template <class T, class Val> bool exist(const T &m, const Val &val) {
  return m.count(val) > 0;
}

template <class It, class T> bool exist(It begin, It end, const T &val) {
  return find(begin, end, val) != end;
}

template <class It, class Pr> bool exist_if(It begin, It end, Pr pred) {
  return find_if(begin, end, pred) != end;
}

template <class T> bool between(T val, T l, T r) {
  return (val >= l) && (val <= r);
}

lint extGCD(lint a, lint b, lint &x, lint &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  lint d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}

template <class It> auto carr(It begin, It end) {
  vec c;
  c.push_back(1);
  auto before = *begin;
  for (auto it = begin + 1; it != end; it++) {
    if (before != *it) {
      c.push_back(0);
      before = *it;
    }
    c.back()++;
  }
  return c;
}

template <class T> struct nval {
  lint n;
  T val;
  nval() : n(0){};
  nval(lint _n, T _val) : n(_n), val(_val){};
};

template <class It> auto carr2(It begin, It end) {
  using T = nval<remove_reference_t<decltype(*begin)>>;

  vect<T> c;
  c.push_back(T(1, *begin));
  auto before = *begin;
  for (auto it = begin + 1; it != end; it++) {
    if (before != *it) {
      c.push_back(T(0, *it));
      before = *it;
    }
    c.back().n++;
  }
  return c;
}

template <class It, class... T> void sort2(It begin, It end, T... p) {
  using val_t = remove_reference_t<decltype(*begin)>;

  sort(begin, end, [p...](const val_t &a, const val_t &b) {
    bool neq[] = {(a.*p != b.*p)...};
    bool sg[] = {(a.*p < b.*p)...};

    rep(i, sizeof...(p)) {
      if (neq[i]) {
        return sg[i];
      }
    }
    return false;
  });
}

template <class It, class It2> auto spacel(It i, It2 end) {
  if (i + 1 == end) {
    return '\\n';
  } else {
    return ' ';
  }
}

bool match(string s, string r) { return regex_match(s, regex(r)); }

ostream &setp(ostream &ost) {
  cout << setprecision(60) << fixed;
  return ost;
}

#ifdef _LOCAL
auto &dbg = cout;
#else
struct dummy_cout {
  template <class T> dummy_cout &operator<<(T &&op) { return *this; }

  using endl_t = basic_ostream<char, char_traits<char>>;

  dummy_cout &operator<<(endl_t &(*)(endl_t &)) { return *this; }
};

dummy_cout dbg;
#endif

const ulint mod = 1000000007;
// const ulint mod = 998244353;
const ld eps = 0.0000001;
}; // namespace

lint dp[100][2];

int main() {

  lint n;
  cin >> n;
  vec a(n);
  rep(i, n) cin >> a[i];

  lint g = 0;
  repi(i, 2, n) g ^= a[i];

  lint s = a[0] + a[1];

  if ((s - g) < 0 || (s - g) % 2 == 1) {
    cout << -1 << endl;
    ret;
  }

  lint c = (s - g) >> 1;

  lint ans = 0, ans_s = -1;

  repr(i, 62) {
    bool cb = c & bit(i), gb = g & bit(i);
    lint nb = (a[0] & bit(i)) != 0;

    lint ans2 = -1, ans_s2 = -1;

    if (cb && gb) {
      cout << -1 << endl;
      ret;
    }
    if (cb && !gb) {
      if (nb == 0) {
        if (ans_s == -1) {
          cout << -1 << endl;
          ret;
        }
        ans2 = ans_s | bit(i);
        ans_s2 = ans_s | bit(i);
      } else {
        ans2 = ans | bit(i);
        if (ans_s != -1)
          ans_s2 = ans_s | bit(i);
      }
    }
    if (!cb && gb) {
      if (nb == 0) {
        ans2 = ans;
        if (ans_s != -1) {
          chmax(ans2, ans_s | bit(i));
          ans_s2 = ans_s | bit(i);
        }
      } else {
        ans2 = ans | bit(i);
        ans_s2 = mmax(ans, ans_s | bit(i));
      }
    }
    if (!cb && !gb) {
      if (nb == 0) {
        ans2 = ans;
        if (ans_s != -1)
          ans_s2 = ans_s;
      } else {
        ans2 = ans;
        ans_s2 = ans;
      }
    }

    ans = ans2;
    ans_s = ans_s2;
  }

  if (ans <= 0) {
    cout << -1 << endl;
    ret;
  }

  cout << a[0] - ans << endl;
  return 0;
}


Error: TLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

#define rep(i, n) for (lint i = 0; i < n; i++)
#define repr(i, n) for (lint i = n - 1; i >= 0; i--)
#define repi(i, ini, n) for (lint i = ini; i < n; i++)
#define repir(i, ini, n) for (lint i = n - 1; i >= ini; i--)
#define repb(i, start, end) for (lint i = start; i <= end; i++)
#define repbr(i, start, end) for (lint i = end; i >= start; i--)

#define bit(n) (1LL << (n))

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rg(v, ini, end) v.begin() + ini, v.begin() + end
#define rrg(v, ini, end) v.rbegin() + ini, v.rbegin() + end

#define ret return 0;

namespace {

using lint = long long;
using ulint = unsigned long long;
using ld = long double;
struct xy {
  lint x, y;
  xy() : x(0), y(0) {}
  xy(lint _x, lint _y) : x(_x), y(_y) {}
  xy operator+(const xy &p) const { return xy(x + p.x, y + p.y); }
  bool operator<(xy p) const {
    if (y == p.y)
      return x < p.x;
    return y < p.y;
  }
};
struct xyd {
  ld x, y;
  xyd() : x(0), y(0) {}
  xyd(long double _x, long double _y) : x(_x), y(_y) {}
};
using vec = vector<lint>;
using vecd = vector<ld>;
using vecs = vector<string>;
using vecp = vector<xy>;
template <class T> using vect = vector<T>;
class vec2 : public vector<vector<lint>> {
public:
  vec2() {}
  vec2(lint n) : vector(n) {}
  vec2(lint h, lint w) : vector(h, vector<lint>(w)) {}
  vec2(lint h, lint w, lint v) : vector(h, vector<lint>(w, v)) {}
};

template <class T> using priq = priority_queue<T>;
template <class T> using rpriq = priority_queue<T, vector<T>, greater<T>>;
template <class Key, class Val> using hashmap = unordered_map<Key, Val>;
template <class Key> using hashset = unordered_set<Key>;

mt19937 mtrand((random_device())());

const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;

template <class T> constexpr auto msum(T arg0) { return arg0; }

template <class T, class... Types> constexpr auto msum(T arg0, Types... args) {
  static_assert(sizeof...(args) > 0, "arg err");

  return arg0 + msum(args...);
}

template <class It> constexpr typename It::value_type mmax(It begin, It end) {
  return *max_element(begin, end);
}

template <class It> constexpr typename It::value_type mmin(It begin, It end) {
  return *min_element(begin, end);
}

template <class T> constexpr auto mmax(T arg) { return arg; }

template <class T, class... Types> constexpr auto mmax(T arg0, Types... args) {
  using promote_t = decltype(msum(arg0, args...));

  return max(static_cast<promote_t>(arg0),
             static_cast<promote_t>(mmax(args...)));
}

template <class T> constexpr auto mmin(T arg) { return arg; }

template <class T, class... Types> constexpr auto mmin(T arg0, Types... args) {
  using promote_t = decltype(msum(arg0, args...));

  return min(static_cast<promote_t>(arg0),
             static_cast<promote_t>(mmin(args...)));
}

template <class T> struct Mplus {
  T operator()(const T &a, const T &b) { return a + b; }

  const static T id = T(0);
};

template <class It, class T = typename It::value_type, class Monoid = Mplus<T>>
T acc(It begin, It end, Monoid f = Mplus<T>()) {
  return accumulate(begin, end, Monoid::id, f);
}

constexpr auto clamp(lint val, lint left, lint right) {
  return mmax(mmin(val, right), left);
}

constexpr lint div2(lint p, lint q) { return (p + q - 1) / q; }

#if (__cplusplus < 201703L)

lint gcd(lint a, lint b) {
  while (1) {
    if (a < b)
      swap(a, b);
    if (!b)
      break;
    a %= b;
  }
  return a;
}

lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }

#endif

constexpr lint powInt(lint a, lint b) {
  if (b == 0) {
    return 1;
  }
  if (b == 1) {
    return a;
  }
  lint tmp = powInt(a, b / 2);
  return (b % 2 == 1 ? a * tmp * tmp : tmp * tmp);
}

template <class T> T sgn(T val) {
  if (val == T(0))
    return T(0);
  if (val < 0)
    return T(-1);
  if (val > 0)
    return T(1);
}

template <class T> constexpr auto modK_belowN(T k, T MOD, T n) {
  return (n + MOD - k - 1) / MOD;
}

template <class It, class T> bool exist(It begin, It end, const T &val) {
  return find(begin, end, val) != end;
}

template <class It, class Pr> bool exist_if(It begin, It end, Pr pred) {
  return find_if(begin, end, pred) != end;
}

template <class T> bool between(T val, T l, T r) {
  return (val >= l) && (val <= r);
}

lint extGCD(lint a, lint b, lint &x, lint &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  lint d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}

template <class It> auto carr(It begin, It end) {
  vec c;
  c.push_back(1);
  auto before = *begin;
  for (auto it = begin + 1; it != end; it++) {
    if (before != *it) {
      c.push_back(0);
      before = *it;
    }
    c.back()++;
  }
  return c;
}

template <class T> struct nval {
  lint n;
  T val;
  nval() : n(0){};
  nval(lint _n, T _val) : n(_n), val(_val){};
};

template <class It> auto carr2(It begin, It end) {
  using T = nval<remove_reference_t<decltype(*begin)>>;

  vect<T> c;
  c.push_back(T(1, *begin));
  auto before = *begin;
  for (auto it = begin + 1; it != end; it++) {
    if (before != *it) {
      c.push_back(T(0, *it));
      before = *it;
    }
    c.back().n++;
  }
  return c;
}

template <class It, class... T> void sort2(It begin, It end, T... p) {
  using val_t = remove_reference_t<decltype(*begin)>;

  sort(begin, end, [p...](const val_t &a, const val_t &b) {
    bool neq[] = {(a.*p != b.*p)...};
    bool sg[] = {(a.*p < b.*p)...};

    rep(i, sizeof...(p)) {
      if (neq[i]) {
        return sg[i];
      }
    }
    return false;
  });
}

template <class It, class It2> auto spacel(It i, It2 end) {
  if (i + 1 == end) {
    return '\\n';
  } else {
    return ' ';
  }
}

bool match(string s, string r) { return regex_match(s, regex(r)); }

ostream &setp(ostream &ost) {
  cout << setprecision(60) << fixed;
  return ost;
}

#ifdef _LOCAL
auto &dbg = cout;
#else
struct dummy_cout {
  template <class T> dummy_cout &operator<<(T &&op) { return *this; }

  using endl_t = basic_ostream<char, char_traits<char>>;

  dummy_cout &operator<<(endl_t &(*)(endl_t &)) { return *this; }
};

dummy_cout dbg;
#endif

const ulint mod = 1000000007;
// const ulint mod = 998244353;
const ld eps = 0.0000001;
}; // namespace

struct mint {
  lint n;
  mint() { n = 0; }
  mint(lint a) { n = a % mod; }
  mint &operator+=(mint a) {
    n += a.n;
    n %= mod;
    return *this;
  }
  mint &operator-=(mint a) {
    n += mod;
    n -= a.n;
    n %= mod;
    return *this;
  }
  mint &operator*=(mint a) {
    n *= a.n;
    n %= mod;
    return *this;
  }
  mint &operator%=(mint a) {
    n %= a.n;
    return *this;
  }
  mint &operator++() {
    n++;
    n %= mod;
    return *this;
  }
  mint &operator--() {
    n += mod;
    n--;
    n %= mod;
    return *this;
  }
};

mint operator+(mint a, mint b) {
  a += b;
  return a;
}
mint operator-(mint a, mint b) {
  a -= b;
  return a;
}
mint operator*(mint a, mint b) {
  a *= b;
  return a;
}

vector<mint> invtbl;
vector<mint> finvtbl;
vector<mint> facttbl;

mint factMod(lint n) {
  if (n == 0) {
    return 1;
  }
  mint ans = 1;
  while (n > 1) {
    ans *= n;
    n--;
  }
  return ans;
}
mint powMod(mint x, lint y) {
  if (x.n <= 1) {
    return x;
  }
  if (y == 0) {
    return 1;
  } else if (y == 1) {
    return x;
  } else if (y % 2 == 0) {
    mint tmp = powMod(x, y / 2);
    return tmp * tmp;
  } else {
    mint tmp = powMod(x, y / 2);
    return tmp * tmp * x;
  }
}
mint modinv(mint n) { return powMod(n, mod - 2); }

void preCalcInv(lint up) {
  invtbl.resize(up + 1);
  invtbl[1] = 1;
  repb(a, 2, up) { invtbl[a] = invtbl[a] = mod - invtbl[mod % a] * (mod / a); }
}

mint operator/(mint a, mint b) {
  if (b.n < invtbl.size()) {
    a *= invtbl[b.n];
  } else {
    a *= modinv(b);
  }
  return a;
}
mint &operator/=(mint &a, mint b) {
  a = a / b;
  return a;
}

void preCalcFactInv(lint up) {
  finvtbl.resize(up + 1);
  finvtbl[0] = 1;
  finvtbl[up] = modinv(factMod(up));
  repbr(a, 1, up - 1) { finvtbl[a] = finvtbl[a + 1] * (a + 1); }
}
void preCalcFact(lint up) {
  facttbl.resize(up + 1);
  facttbl[0] = 1;
  repb(a, 1, up) { facttbl[a] = facttbl[a - 1] * a; }
}
void preCalc(lint up) {
  invtbl.resize(up + 1);
  finvtbl.resize(up + 1);
  facttbl.resize(up + 1);
  invtbl[1] = 1;
  facttbl[0] = facttbl[1] = 1;
  finvtbl[0] = finvtbl[1] = 1;
  repb(a, 2, up) {
    facttbl[a] = facttbl[a - 1] * a;
    invtbl[a] = invtbl[a] = mod - invtbl[mod % a] * (mod / a);
    finvtbl[a] = finvtbl[a - 1] * invtbl[a];
  }
}

mint factModInv(lint a) {
  if (a < finvtbl.size()) {
    return finvtbl[a];
  } else {
    return modinv(factMod(a));
  }
}
mint nCrMod(lint n, lint r) {
  if (n < r || n < 0 || r < 0) {
    return 0;
  }
  r = mmin(r, n - r);
  mint a = 1;
  if (n < finvtbl.size() && n < facttbl.size()) {
    a *= facttbl[n];
    a *= finvtbl[r];
    a *= finvtbl[n - r];
    return a;
  } else {
    repb(i, n - r + 1, n) { a *= i; }
    a *= factModInv(r);
    return a;
  }
}
mint nHrMod(lint n, lint r) { return nCrMod(n + r - 1, r); }

int main() {
  lint n;
  cin >> n;

  vec a(n);
  rep(i, n) cin >> a[i];

  lint x = 0;
  repi(i, 2, n) x ^= a[i];

  rep(s, a[0]) {
    if (((a[0] - s) ^ (a[1] + s)) == x) {
      cout << s << endl;
      ret;
    }
  }

  cout << -1 << endl;

  return 0;
}