Problem p03569 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#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 brep(i, n) rep(i, bit(n))
#define brepi(i, ini, n) repi(i, ini, bit(n))

#define len(a) (static_cast<lint>(a.size()))

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

#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>>;

// const ulint mod = 1000000007;
const ulint mod = 998244353;
const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;
const ld eps = 0.0000001;
const lint alpn = 'z' - 'a' + 1;

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

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);
}

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...](val_t a, 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 <size_t _K, size_t _N, class... Types, size_t... indices>
auto constexpr __ModKtuple_Impl(index_sequence<indices...>,
                                tuple<Types...> args) {
  return make_tuple(get<indices * _N + _K>(args)...);
}

template <size_t K, size_t N, class... Types>
auto constexpr ModKtuple(Types... args) {
  return __ModKtuple_Impl<K, N>(
      make_index_sequence<modK_belowN(K, N, sizeof...(args))>{},
      forward_as_tuple(args...));
}

template <class It, class... T, class... Tsg, size_t... indices>
void __sort3_Impl(It begin, It end, tuple<T...> p, tuple<Tsg...> sgf,
                  index_sequence<indices...>) {
  using val_t = remove_reference_t<decltype(*begin)>;

  sort(begin, end, [p, sgf](val_t a, val_t b) {
    bool neq[] = {(a.*(get<indices>(p)) != b.*(get<indices>(p)))...};
    bool sg[] = {((a.*(get<indices>(p)) < b.*(get<indices>(p))) !=
                  (get<indices>(sgf)))...};

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

template <class It, class... T> void sort3(It begin, It end, T... p) {
  using val_t = remove_reference_t<decltype(*begin)>;

  auto p_forward = ModKtuple<0, 2>(p...);
  auto sgf_forward = ModKtuple<1, 2>(p...);

  constexpr auto p_sz = tuple_size<decltype(p_forward)>::value;
  constexpr auto sgf_sz = tuple_size<decltype(sgf_forward)>::value;

  static_assert(p_sz == sgf_sz, "arg err");

  __sort3_Impl(begin, end, p_forward, sgf_forward, make_index_sequence<p_sz>{});
}

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)); }

template <class It> bool next_comb(lint n, It begin, It end) {
  auto rend = make_reverse_iterator(begin);
  auto rbegin = make_reverse_iterator(end);

  auto rit = rbegin;
  for (; rit != rend; rit++) {
    if ((rit == rbegin && (*rit) + 1 != n) ||
        (rit != rbegin && (*rit) + 1 != *(rit - 1))) {
      goto found;
    }
  }
  return false;
found:;
  (*rit)++;

  for (auto it = rit.base(); it != end; it++) {
    (*it) = (*(it - 1)) + 1;
  }
  return true;
}

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
}; // namespace

int main() {
  string s;
  cin >> s;

  vec p(s.length(), -1);

  string sx;
  rep(i, s.length()) {
    if (s[i] != 'x') {
      p[sx.size()] = i;
      sx.push_back(s[i]);
    }
  }

  string sx2 = sx;
  reverse(all(sx2));
  if (sx != sx2) {
    cout << -1 << endl;
    ret;
  }

  lint l, r;
  if (sx.length() % 2 == 1) {
    l = p[sx.length() / 2];
    r = p[sx.length() / 2];
  } else {
    l = p[sx.length() / 2 - 1];
    r = p[sx.length() / 2];
  }

  s = "-"s + s + "-"s;
  l++;
  r++;

  lint ans = 0;
  while (1) {
    if (s[l] != '-')
      l--;
    if (s[r] != '-')
      r++;
    if (s[l] == '-' && s[r] == '-')
      break;
    if (s[l] != s[r]) {
      if (s[l] == 'x') {
        while (s[l] != '-' && s[l] != s[r]) {
          l--;
          ans++;
        }
      }

      if (s[r] == 'x') {
        while (s[r] != '-' && s[l] != s[r]) {
          r++;
          ans++;
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#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 brep(i, n) rep(i, bit(n))
#define brepi(i, ini, n) repi(i, ini, bit(n))

#define len(a) (static_cast<lint>(a.size()))

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

#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>>;

// const ulint mod = 1000000007;
const ulint mod = 998244353;
const double pi = 3.141592653589793238462;
const lint intmax = 9223372036854775807;
const lint inf = 1100100100100100100LL;
const ld eps = 0.0000001;
const lint alpn = 'z' - 'a' + 1;

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

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);
}

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...](val_t a, 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 <size_t _K, size_t _N, class... Types, size_t... indices>
auto constexpr __ModKtuple_Impl(index_sequence<indices...>,
                                tuple<Types...> args) {
  return make_tuple(get<indices * _N + _K>(args)...);
}

template <size_t K, size_t N, class... Types>
auto constexpr ModKtuple(Types... args) {
  return __ModKtuple_Impl<K, N>(
      make_index_sequence<modK_belowN(K, N, sizeof...(args))>{},
      forward_as_tuple(args...));
}

template <class It, class... T, class... Tsg, size_t... indices>
void __sort3_Impl(It begin, It end, tuple<T...> p, tuple<Tsg...> sgf,
                  index_sequence<indices...>) {
  using val_t = remove_reference_t<decltype(*begin)>;

  sort(begin, end, [p, sgf](val_t a, val_t b) {
    bool neq[] = {(a.*(get<indices>(p)) != b.*(get<indices>(p)))...};
    bool sg[] = {((a.*(get<indices>(p)) < b.*(get<indices>(p))) !=
                  (get<indices>(sgf)))...};

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

template <class It, class... T> void sort3(It begin, It end, T... p) {
  using val_t = remove_reference_t<decltype(*begin)>;

  auto p_forward = ModKtuple<0, 2>(p...);
  auto sgf_forward = ModKtuple<1, 2>(p...);

  constexpr auto p_sz = tuple_size<decltype(p_forward)>::value;
  constexpr auto sgf_sz = tuple_size<decltype(sgf_forward)>::value;

  static_assert(p_sz == sgf_sz, "arg err");

  __sort3_Impl(begin, end, p_forward, sgf_forward, make_index_sequence<p_sz>{});
}

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)); }

template <class It> bool next_comb(lint n, It begin, It end) {
  auto rend = make_reverse_iterator(begin);
  auto rbegin = make_reverse_iterator(end);

  auto rit = rbegin;
  for (; rit != rend; rit++) {
    if ((rit == rbegin && (*rit) + 1 != n) ||
        (rit != rbegin && (*rit) + 1 != *(rit - 1))) {
      goto found;
    }
  }
  return false;
found:;
  (*rit)++;

  for (auto it = rit.base(); it != end; it++) {
    (*it) = (*(it - 1)) + 1;
  }
  return true;
}

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
}; // namespace

int main() {
  string s;
  cin >> s;

  vec p(s.length(), -1);

  string sx;
  rep(i, s.length()) {
    if (s[i] != 'x') {
      p[sx.size()] = i;
      sx.push_back(s[i]);
    }
  }

  string sx2 = sx;
  reverse(all(sx2));
  if (sx != sx2) {
    cout << -1 << endl;
    ret;
  }
  if (sx.size() == 0) {
    cout << 0 << endl;
    ret;
  }

  lint l, r;
  if (sx.length() % 2 == 1) {
    l = p[sx.length() / 2];
    r = p[sx.length() / 2];
  } else {
    l = p[sx.length() / 2 - 1];
    r = p[sx.length() / 2];
  }

  s = "-"s + s + "-"s;
  l++;
  r++;

  lint ans = 0;
  while (1) {
    if (s[l] != '-')
      l--;
    if (s[r] != '-')
      r++;
    if (s[l] == '-' && s[r] == '-')
      break;
    if (s[l] != s[r]) {
      if (s[l] == 'x') {
        while (s[l] != '-' && s[l] != s[r]) {
          l--;
          ans++;
        }
      }

      if (s[r] == 'x') {
        while (s[r] != '-' && s[l] != s[r]) {
          r++;
          ans++;
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}