Problem p02939 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define GET_MACRO(_1, _2, _3, _4, _5, _6, _7, _8, NAME, ...) NAME
#define pr(...)                                                                \
  cerr << GET_MACRO(__VA_ARGS__, pr8, pr7, pr6, pr5, pr4, pr3, pr2,            \
                    pr1)(__VA_ARGS__)                                          \
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define prArr(a)                                                               \
  {                                                                            \
    cerr << (#a) << "={";                                                      \
    int i = 0;                                                                 \
    for (auto t : (a))                                                         \
      cerr << (i++ ? ", " : "") << t;                                          \
    cerr << "}" << endl;                                                       \
  }
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;

const Int mod = (1e9) + 7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE
_int used[2][200010], mem[2][200010];
const Int INF = 1e9; // ~ 1.15 * 1e18
signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  string str;
  cin >> str;
  Int N = str.size();

  const Int null = 29;
  function<Int(Int, Int)> dfs = [&](Int len, Int idx) {
    if (idx == N)
      return 0;
    if (used[len][idx]++)
      return mem[len][idx];

    Int a = -INF, b = -INF;
    char p1 = len == 2 ? str[idx - 2] - 'a' : 29;
    char p2 = idx > 0 ? str[idx - 1] - 'a' : 29;

    if (idx + 1 <= N) {
      Int ch1 = null;
      Int ch2 = str[idx] - 'a';
      if (p1 != ch1 || p2 != ch2)
        a = dfs(1, idx + 1) + 1;
    }

    if (idx + 2 <= N) {
      Int ch1 = str[idx] - 'a';
      Int ch2 = str[idx + 1] - 'a';
      if (p1 != ch1 || p2 != ch2)
        b = dfs(2, idx + 2) + 1;
    }
    Int res = max(a, b);
    return mem[len][idx] = res;
  };

  Int ans = dfs(0, 0);
  cout << ans << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define GET_MACRO(_1, _2, _3, _4, _5, _6, _7, _8, NAME, ...) NAME
#define pr(...)                                                                \
  cerr << GET_MACRO(__VA_ARGS__, pr8, pr7, pr6, pr5, pr4, pr3, pr2,            \
                    pr1)(__VA_ARGS__)                                          \
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define prArr(a)                                                               \
  {                                                                            \
    cerr << (#a) << "={";                                                      \
    int i = 0;                                                                 \
    for (auto t : (a))                                                         \
      cerr << (i++ ? ", " : "") << t;                                          \
    cerr << "}" << endl;                                                       \
  }
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;

const Int mod = (1e9) + 7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE
_int used[3][200010], mem[3][200010];
const Int INF = 1e9; // ~ 1.15 * 1e18
signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  string str;
  cin >> str;
  Int N = str.size();

  const Int null = 29;
  function<Int(Int, Int)> dfs = [&](Int len, Int idx) {
    if (idx == N)
      return 0;
    if (used[len][idx]++)
      return mem[len][idx];

    Int a = -INF, b = -INF;
    char p1 = len == 2 ? str[idx - 2] - 'a' : 29;
    char p2 = idx > 0 ? str[idx - 1] - 'a' : 29;

    if (idx + 1 <= N) {
      Int ch1 = null;
      Int ch2 = str[idx] - 'a';
      if (p1 != ch1 || p2 != ch2)
        a = dfs(1, idx + 1) + 1;
    }

    if (idx + 2 <= N) {
      Int ch1 = str[idx] - 'a';
      Int ch2 = str[idx + 1] - 'a';
      if (p1 != ch1 || p2 != ch2)
        b = dfs(2, idx + 2) + 1;
    }
    Int res = max(a, b);
    return mem[len][idx] = res;
  };

  Int ans = dfs(0, 0);
  cout << ans << endl;
  return 0;
}