Problem p03357 (C++)

Buggy submission (status: Runtime Error):
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename Container> int SZ(const Container &S) { return S.size(); }

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg_var(x) clog << #x << ": " << x << endl;
#define dbg_array(x, len)                                                      \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg_var(x)
#define dbg_array(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

const int MAXN = 2010;
int cw[MAXN][MAXN];
int cb[MAXN][MAXN];
int ccw[MAXN], ccb[MAXN];
int din[MAXN][MAXN];

char c[MAXN];
int a[MAXN];

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!
  int N;
  cin >> N;
  for (int i = 1; i <= 2 * N; i++)
    cin >> c[i] >> a[i];
  for (int j = 0; j <= N; j++) {
    int black_num = 0;
    int white_num = 0;
    for (int it = 2 * N; it >= 1; it--) {
      if (c[it] == 'W') {
        cw[a[it]][j] = black_num;
        if (a[it] == j + 1)
          ccw[a[it]] = white_num;
        white_num += (a[it] <= j);
      } else if (c[it] == 'B') {
        cb[a[it]][j] = white_num;
        black_num += (a[it] <= j);
        if (a[it] == j + 1)
          ccb[a[it]] = black_num;
      }
    }
  }
  // for (int j = 0; j <= N; j++) {
  // dbg_var(j);
  // for (int i = 1; i <= N; i++) cout << cw[i][j] << "\n";
  // }
  // return 0;
  for (int i = 0; i <= N; i++)
    for (int j = 0; j <= N; j++) {
      if (i == 0 and j == 0)
        continue;
      if (i == 0)
        din[i][j] = din[i][j - 1] + cb[j][i] + ccb[j];
      else if (j == 0)
        din[i][j] = din[i - 1][j] + cw[i][j] + ccw[i];
      else
        din[i][j] = min(din[i][j - 1] + cb[j][i] + ccb[j],
                        din[i - 1][j] + cw[i][j] + ccw[i]);
    }
  cout << din[N][N] << "\n";
}


Fixed submission:
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename Container> int SZ(const Container &S) { return S.size(); }

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg_var(x) clog << #x << ": " << x << endl;
#define dbg_array(x, len)                                                      \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg_var(x)
#define dbg_array(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

const int MAXN = 2010;
int cw[MAXN][MAXN];
int cb[MAXN][MAXN];
int ccw[MAXN], ccb[MAXN];
int din[MAXN][MAXN];

char c[MAXN * 2];
int a[MAXN * 2];

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!
  int N;
  cin >> N;
  for (int i = 1; i <= 2 * N; i++)
    cin >> c[i] >> a[i];
  for (int j = 0; j <= N; j++) {
    int black_num = 0;
    int white_num = 0;
    for (int it = 2 * N; it >= 1; it--) {
      if (c[it] == 'W') {
        cw[a[it]][j] = black_num;
        if (a[it] == j + 1)
          ccw[a[it]] = white_num;
        white_num += (a[it] <= j);
      } else if (c[it] == 'B') {
        cb[a[it]][j] = white_num;
        black_num += (a[it] <= j);
        if (a[it] == j + 1)
          ccb[a[it]] = black_num;
      }
    }
  }
  // for (int j = 0; j <= N; j++) {
  // dbg_var(j);
  // for (int i = 1; i <= N; i++) cout << cw[i][j] << "\n";
  // }
  // return 0;
  for (int i = 0; i <= N; i++)
    for (int j = 0; j <= N; j++) {
      if (i == 0 and j == 0)
        continue;
      if (i == 0)
        din[i][j] = din[i][j - 1] + cb[j][i] + ccb[j];
      else if (j == 0)
        din[i][j] = din[i - 1][j] + cw[i][j] + ccw[i];
      else
        din[i][j] = min(din[i][j - 1] + cb[j][i] + ccb[j],
                        din[i - 1][j] + cw[i][j] + ccw[i]);
    }
  cout << din[N][N] << "\n";
}