Problem p03357 (C++)

Buggy submission (status: Runtime Error):
/*{{{*/
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define REP(I, N) for (int I = 0; I < (N); ++I)
#define REPP(I, A, B) for (int I = (A); I < (B); ++I)
#define FOR(I, A, B) for (int I = (A); I <= (B); ++I)
#define FORS(I, S) for (int I = 0; S[I]; ++I)
#define RS(X) scanf("%s", (X))
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define CASET                                                                  \
  int ___T;                                                                    \
  scanf("%d", &___T);                                                          \
  for (int cs = 1; cs <= ___T; cs++)
#define MP make_pair
#define PB push_back
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define LEN(X) strlen(X)
#define F first
#define S second
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef long double LD;
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<PII> VPII;
typedef pair<LL, LL> PLL;
typedef vector<PLL> VPLL;
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%lld", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T, class U> void _W(const pair<T, U> &x) {
  _W(x.F);
  putchar(' ');
  _W(x.S);
}
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
#ifdef HOME
#define DEBUG(...)                                                             \
  {                                                                            \
    printf("# ");                                                              \
    printf(__VA_ARGS__);                                                       \
    puts("");                                                                  \
  }
#else
#define DEBUG(...)
#endif
int MOD = 1e9 + 7;
void ADD(LL &x, LL v) {
  x = (x + v) % MOD;
  if (x < 0)
    x += MOD;
}
/*}}}*/
const int SIZE = 2010;
struct BIT {
  int _n;
  LL _d[SIZE];
  void init(int __n) {
    _n = __n;
    memset(_d, 0, sizeof(LL) * (_n + 1));
  }
  void ins(int x, LL v) {
    for (; x <= _n; x += x & -x)
      _d[x] += v;
  }
  LL qq(int x) {
    LL res = 0;
    for (; x; x -= x & -x)
      res += _d[x];
    return res;
  }
  LL qq_range(int x, int y) {
    LL ret = qq(y);
    if (x)
      ret -= qq(x - 1);
    return ret;
  }
} bit;
// TODO init
int p[2][SIZE], dp[SIZE][SIZE];
int main() {
  int N;
  R(N);
  FOR(i, 1, N * 2) {
    char s[4];
    int x;
    RS(s);
    R(x);
    if (s[0] == 'W')
      p[0][x] = i;
    else
      p[1][x] = i;
  }
  FOR(i, 0, N) FOR(j, 0, N) dp[i][j] = MOD;
  dp[0][0] = 0;
  FOR(i, 0, N) {
    bit.init(2 * N);
    FOR(j, 1, i) bit.ins(p[0][j], 1);
    FOR(j, 0, N) {
      if (j)
        bit.ins(p[1][j], 1);
      int need;
      if (i < N) {
        need = p[0][i + 1] - 1 - bit.qq(p[0][i + 1] - 1);
        dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + need);
      }
      if (j < N) {
        need = p[1][j + 1] - 1 - bit.qq(p[1][j + 1] - 1);
        dp[i][j + 1] = min(dp[i][j + 1], dp[i][j] + need);
      }
    }
  }
  W(dp[N][N]);
  return 0;
}


Fixed submission:
/*{{{*/
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define REP(I, N) for (int I = 0; I < (N); ++I)
#define REPP(I, A, B) for (int I = (A); I < (B); ++I)
#define FOR(I, A, B) for (int I = (A); I <= (B); ++I)
#define FORS(I, S) for (int I = 0; S[I]; ++I)
#define RS(X) scanf("%s", (X))
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define CASET                                                                  \
  int ___T;                                                                    \
  scanf("%d", &___T);                                                          \
  for (int cs = 1; cs <= ___T; cs++)
#define MP make_pair
#define PB push_back
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define LEN(X) strlen(X)
#define F first
#define S second
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef long double LD;
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<PII> VPII;
typedef pair<LL, LL> PLL;
typedef vector<PLL> VPLL;
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%lld", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T, class U> void _W(const pair<T, U> &x) {
  _W(x.F);
  putchar(' ');
  _W(x.S);
}
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
#ifdef HOME
#define DEBUG(...)                                                             \
  {                                                                            \
    printf("# ");                                                              \
    printf(__VA_ARGS__);                                                       \
    puts("");                                                                  \
  }
#else
#define DEBUG(...)
#endif
int MOD = 1e9 + 7;
void ADD(LL &x, LL v) {
  x = (x + v) % MOD;
  if (x < 0)
    x += MOD;
}
/*}}}*/
const int SIZE = 4010;
struct BIT {
  int _n;
  LL _d[SIZE];
  void init(int __n) {
    _n = __n;
    memset(_d, 0, sizeof(LL) * (_n + 1));
  }
  void ins(int x, LL v) {
    for (; x <= _n; x += x & -x)
      _d[x] += v;
  }
  LL qq(int x) {
    LL res = 0;
    for (; x; x -= x & -x)
      res += _d[x];
    return res;
  }
  LL qq_range(int x, int y) {
    LL ret = qq(y);
    if (x)
      ret -= qq(x - 1);
    return ret;
  }
} bit;
// TODO init
int p[2][SIZE], dp[SIZE][SIZE];
int main() {
  int N;
  R(N);
  FOR(i, 1, N * 2) {
    char s[4];
    int x;
    RS(s);
    R(x);
    if (s[0] == 'W')
      p[0][x] = i;
    else
      p[1][x] = i;
  }
  FOR(i, 0, N) FOR(j, 0, N) dp[i][j] = MOD;
  dp[0][0] = 0;
  FOR(i, 0, N) {
    bit.init(2 * N);
    FOR(j, 1, i) bit.ins(p[0][j], 1);
    FOR(j, 0, N) {
      if (j)
        bit.ins(p[1][j], 1);
      int need;
      if (i < N) {
        need = p[0][i + 1] - 1 - bit.qq(p[0][i + 1] - 1);
        dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + need);
      }
      if (j < N) {
        need = p[1][j + 1] - 1 - bit.qq(p[1][j + 1] - 1);
        dp[i][j + 1] = min(dp[i][j + 1], dp[i][j] + need);
      }
    }
  }
  W(dp[N][N]);
  return 0;
}