Problem p03570 (C++)

Buggy submission (status: Time Limit Exceeded):
#pragma GCC optimize("O3")

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>

namespace fastinput {
/** Interface */

template <class T = int> inline T readInt();
inline long double readDouble();
inline int readUInt();
inline int readChar();
inline void readWord(char *s);
inline bool readLine(char *s); // do not save '\n'
inline bool isEof();
inline int peekChar();
inline bool seekEof();

template <class T> inline void writeInt(T x, int len = -1);
template <class T> inline void writeUInt(T x, int len = -1);
inline void writeChar(int x);
inline void writeWord(const char *s);
inline void writeDouble(long int x, int len = 0);
inline void flush();

/** Read */

static const int buf_size = 4096;

static char buf[buf_size];
static int buf_len = 0, buf_pos = 0;

inline bool isEof() {
  if (buf_pos == buf_len) {
    buf_pos = 0, buf_len = fread(buf, 1, buf_size, stdin);
    if (buf_pos == buf_len)
      return 1;
  }
  return 0;
}

inline int getChar() { return isEof() ? -1 : buf[buf_pos++]; }

inline int peekChar() { return isEof() ? -1 : buf[buf_pos]; }

inline bool seekEof() {
  int c;
  while ((c = peekChar()) != -1 && c <= 32)
    buf_pos++;
  return c == -1;
}

inline int readChar() {
  int c = getChar();
  while (c != -1 && c <= 32)
    c = getChar();
  return c;
}

inline int readUInt() {
  int c = readChar(), x = 0;
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return x;
}

template <class T> inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}

inline long double readDouble() {
  int s = 1, c = readChar();
  long double x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  if (c == '.') {
    c = getChar();
    long double coef = 1;
    while ('0' <= c && c <= '9')
      x += (c - '0') * (coef *= 0.1), c = getChar();
  }
  return s == 1 ? x : -x;
}

inline void readWord(char *s) {
  int c = readChar();
  while (c > 32)
    *s++ = (char)c, c = getChar();
  *s = 0;
}

inline bool readLine(char *s) {
  int c = getChar();
  while (c != '\n' && c != -1)
    *s++ = (char)c, c = getChar();
  *s = 0;
  return c != -1;
}

/** Write */

static int write_buf_pos = 0;
static char write_buf[buf_size];

inline void writeChar(int x) {
  if (write_buf_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_buf_pos = 0;
  write_buf[write_buf_pos++] = (char)x;
}

inline void flush() {
  if (write_buf_pos)
    fwrite(write_buf, 1, write_buf_pos, stdout), write_buf_pos = 0;
}

template <class T> inline void writeInt(T x, int output_len) {
  if (x < 0)
    writeChar('-'), x = -x;

  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len)
    s[n++] = '0';
  while (n--)
    writeChar(s[n]);
}

template <class T> inline void writeUInt(T x, int output_len) {
  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len)
    s[n++] = '0';
  while (n--)
    writeChar(s[n]);
}

inline void writeWord(const char *s) {
  while (*s)
    writeChar(*s++);
}

inline void writeDouble(long int x, int output_len) {
  if (x < 0)
    writeChar('-'), x = -x;
  int t = (int)x;
  writeUInt(t), x -= t;
  writeChar('.');
  for (int i = output_len - 1; i > 0; i--) {
    x *= 10;
    t = std::min(9, (int)x);
    writeChar('0' + t), x -= t;
  }
  x *= 10;
  t = std::min(9, (int)(x + 0.5));
  writeChar('0' + t);
}
} // namespace fastinput

using namespace fastinput;
using namespace std;

///** Begin fast allocation */
// const int MAX_MEM = 64e6;
// int mpos = 0;
// char mem[MAX_MEM];
// inline void * operator new (size_t n) {
//   mpos += n;
//   return (void *)(mem + mpos - n);
// }
// inline void operator delete (void *) noexcept {} // must have!
//                                                /** End fast allocation */

const int N = 2e5 + 10;
const int ANTIBADTEST = 1200;
const int ALPHABET = 26;
int masked[1 << ALPHABET];
int masks[N];
int dp[N];

int popcnt(int x) {
  int keep = 0;
  while (x) {
    x = x & (x - 1);
    ++keep;
  }
  return keep;
}

int answerFast(string s) {
  int n = s.length();
  int curmask = 0;
  memset(masked, -1, sizeof(masked));
  masks[0] = 0;
  masked[0] = 0;
  map<char, int> mp;
  for (int i = 0; i < n; ++i) {
    mp[s[i]] = 1;
  }
  for (int i = 0; i <= n; ++i)
    dp[i] = i;
  for (int i = 0; i < n; ++i) {
    curmask ^= 1 << (s[i] - 'a');
    for (int j = 0; j < ALPHABET; ++j) {
      int shifted =
          curmask ^
          (1 << j); // there MUST always be singular letter, otherwise merge.
      if (masked[shifted] != -1) {
        int go = masked[shifted];
        dp[i + 1] = min(dp[i + 1], dp[go] + 1);
      }
    }
    masks[i + 1] = curmask;
    masked[curmask] = i + 1;
  }
  for (int i = 0; i < n; ++i)
    dp[i + 1] = min(dp[i + 1], dp[i] + 1);
  if (popcnt(masks[n]) <= 1) {
    return 1;
  }
  for (int i = 0; i < n; ++i) {
    int pr = masks[i];
    int go = -1;
    for (int j = 0; j < ALPHABET; ++j) {
      int shifted =
          pr ^
          (1 << j); // there MUST always be singular letter, otherwise merge.
      if (masked[shifted] != -1) {
        int go = masked[shifted];
        dp[go] = min(dp[go], dp[i] + 1);
      }
    }
    for (int shifter = 0; shifter < ANTIBADTEST && i + shifter <= n;
         ++shifter) {
      if (popcnt(masks[i + shifter] ^ pr) <= 1) {
        dp[i + shifter] = min(dp[i + shifter], dp[i] + 1);
      }
    }
  }
  return dp[n];
}

int main() {
  string s;
  cin >> s;
  cout << answerFast(s) << endl;
  return 0;
}

Fixed submission:
#pragma GCC optimize("O3")

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>

namespace fastinput {
/** Interface */

template <class T = int> inline T readInt();
inline long double readDouble();
inline int readUInt();
inline int readChar();
inline void readWord(char *s);
inline bool readLine(char *s); // do not save '\n'
inline bool isEof();
inline int peekChar();
inline bool seekEof();

template <class T> inline void writeInt(T x, int len = -1);
template <class T> inline void writeUInt(T x, int len = -1);
inline void writeChar(int x);
inline void writeWord(const char *s);
inline void writeDouble(long int x, int len = 0);
inline void flush();

/** Read */

static const int buf_size = 4096;

static char buf[buf_size];
static int buf_len = 0, buf_pos = 0;

inline bool isEof() {
  if (buf_pos == buf_len) {
    buf_pos = 0, buf_len = fread(buf, 1, buf_size, stdin);
    if (buf_pos == buf_len)
      return 1;
  }
  return 0;
}

inline int getChar() { return isEof() ? -1 : buf[buf_pos++]; }

inline int peekChar() { return isEof() ? -1 : buf[buf_pos]; }

inline bool seekEof() {
  int c;
  while ((c = peekChar()) != -1 && c <= 32)
    buf_pos++;
  return c == -1;
}

inline int readChar() {
  int c = getChar();
  while (c != -1 && c <= 32)
    c = getChar();
  return c;
}

inline int readUInt() {
  int c = readChar(), x = 0;
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return x;
}

template <class T> inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}

inline long double readDouble() {
  int s = 1, c = readChar();
  long double x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  if (c == '.') {
    c = getChar();
    long double coef = 1;
    while ('0' <= c && c <= '9')
      x += (c - '0') * (coef *= 0.1), c = getChar();
  }
  return s == 1 ? x : -x;
}

inline void readWord(char *s) {
  int c = readChar();
  while (c > 32)
    *s++ = (char)c, c = getChar();
  *s = 0;
}

inline bool readLine(char *s) {
  int c = getChar();
  while (c != '\n' && c != -1)
    *s++ = (char)c, c = getChar();
  *s = 0;
  return c != -1;
}

/** Write */

static int write_buf_pos = 0;
static char write_buf[buf_size];

inline void writeChar(int x) {
  if (write_buf_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_buf_pos = 0;
  write_buf[write_buf_pos++] = (char)x;
}

inline void flush() {
  if (write_buf_pos)
    fwrite(write_buf, 1, write_buf_pos, stdout), write_buf_pos = 0;
}

template <class T> inline void writeInt(T x, int output_len) {
  if (x < 0)
    writeChar('-'), x = -x;

  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len)
    s[n++] = '0';
  while (n--)
    writeChar(s[n]);
}

template <class T> inline void writeUInt(T x, int output_len) {
  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len)
    s[n++] = '0';
  while (n--)
    writeChar(s[n]);
}

inline void writeWord(const char *s) {
  while (*s)
    writeChar(*s++);
}

inline void writeDouble(long int x, int output_len) {
  if (x < 0)
    writeChar('-'), x = -x;
  int t = (int)x;
  writeUInt(t), x -= t;
  writeChar('.');
  for (int i = output_len - 1; i > 0; i--) {
    x *= 10;
    t = std::min(9, (int)x);
    writeChar('0' + t), x -= t;
  }
  x *= 10;
  t = std::min(9, (int)(x + 0.5));
  writeChar('0' + t);
}
} // namespace fastinput

using namespace fastinput;
using namespace std;

///** Begin fast allocation */
// const int MAX_MEM = 64e6;
// int mpos = 0;
// char mem[MAX_MEM];
// inline void * operator new (size_t n) {
//   mpos += n;
//   return (void *)(mem + mpos - n);
// }
// inline void operator delete (void *) noexcept {} // must have!
//                                                /** End fast allocation */

const int N = 2e5 + 10;
const int ANTIBADTEST = 1100;
const int ALPHABET = 26;
int masked[1 << ALPHABET];
int masks[N];
int dp[N];

int popcnt(int x) {
  int keep = 0;
  while (x) {
    x = x & (x - 1);
    ++keep;
  }
  return keep;
}

int answerFast(string s) {
  int n = s.length();
  int curmask = 0;
  memset(masked, -1, sizeof(masked));
  masks[0] = 0;
  masked[0] = 0;
  map<char, int> mp;
  for (int i = 0; i < n; ++i) {
    mp[s[i]] = 1;
  }
  for (int i = 0; i <= n; ++i)
    dp[i] = i;
  for (int i = 0; i < n; ++i) {
    curmask ^= 1 << (s[i] - 'a');
    for (int j = 0; j < ALPHABET; ++j) {
      int shifted =
          curmask ^
          (1 << j); // there MUST always be singular letter, otherwise merge.
      if (masked[shifted] != -1) {
        int go = masked[shifted];
        dp[i + 1] = min(dp[i + 1], dp[go] + 1);
      }
    }
    masks[i + 1] = curmask;
    masked[curmask] = i + 1;
  }
  for (int i = 0; i < n; ++i)
    dp[i + 1] = min(dp[i + 1], dp[i] + 1);
  if (popcnt(masks[n]) <= 1) {
    return 1;
  }
  for (int i = 0; i < n; ++i) {
    int pr = masks[i];
    int go = -1;
    for (int j = 0; j < ALPHABET; ++j) {
      int shifted =
          pr ^
          (1 << j); // there MUST always be singular letter, otherwise merge.
      if (masked[shifted] != -1) {
        int go = masked[shifted];
        dp[go] = min(dp[go], dp[i] + 1);
      }
    }
    for (int shifter = 0; shifter < ANTIBADTEST && i + shifter <= n;
         ++shifter) {
      if (popcnt(masks[i + shifter] ^ pr) <= 1) {
        dp[i + shifter] = min(dp[i + shifter], dp[i] + 1);
      }
    }
  }
  return dp[n];
}

int main() {
  string s;
  cin >> s;
  cout << answerFast(s) << endl;
  return 0;
}