Problem p03081 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define rep(i, N) for (int i = 0, i##_max = (N); i < i##_max; ++i)
#define repp(i, l, r) for (int i = (l), i##_max = (r); i < i##_max; ++i)
#define per(i, N) for (int i = (N)-1; i >= 0; --i)
#define perr(i, l, r) for (int i = r - 1, i##_min(l); i >= i##_min; --i)
#define all(arr) (arr).begin(), (arr).end()
#define SP << " " <<
#define SPF << " "
#define SPEEDUP                                                                \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);
#define MAX_I INT_MAX      // 1e9
#define MIN_I INT_MIN      //-1e9
#define MAX_UI UINT_MAX    // 1e9
#define MAX_LL LLONG_MAX   // 1e18
#define MIN_LL LLONG_MIN   //-1e18
#define MAX_ULL ULLONG_MAX // 1e19
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<char, char> PCC;
typedef pair<ll, ll> PLL;
typedef pair<char, int> PCI;
typedef pair<int, char> PIC;
typedef pair<ll, int> PLI;
typedef pair<int, ll> PIL;
typedef pair<ll, char> PLC;
typedef pair<char, ll> PCL;

inline void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
inline void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
inline void Yay(bool b) { cout << (b ? "Yay!" : ":(") << endl; }

string s;
vector<PCC> v;
int N, Q;
int move(int pos) {
  rep(i, Q) {
    if (s[pos] == v[i].first) {
      if (v[i].second == 'L')
        --pos;
      else
        ++pos;
    }
  }
  return pos;
}

int main(void) {
  SPEEDUP
  cout << setprecision(15);
  cin >> N >> Q;
  cin >> s;
  s = " " + s + " ";
  v.resize(N);
  rep(i, Q) cin >> v[i].first >> v[i].second;
  // 左に落ちる最大の位置
  int ls = 0, le = N + 1;
  while (le - ls > 1) {
    int lm = (ls + le) / 2;
    if (move(lm) == 0)
      ls = lm;
    else
      le = lm;
  }

  // 右に落ちる最小の位置
  int rs = 0, re = N + 1;
  while (re - rs > 1) {
    int rm = (rs + re) / 2;
    if (move(rm) == N + 1)
      re = rm;
    else
      rs = rm;
  }
  cout << N - ls - (N + 1 - re) << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define rep(i, N) for (int i = 0, i##_max = (N); i < i##_max; ++i)
#define repp(i, l, r) for (int i = (l), i##_max = (r); i < i##_max; ++i)
#define per(i, N) for (int i = (N)-1; i >= 0; --i)
#define perr(i, l, r) for (int i = r - 1, i##_min(l); i >= i##_min; --i)
#define all(arr) (arr).begin(), (arr).end()
#define SP << " " <<
#define SPF << " "
#define SPEEDUP                                                                \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);
#define MAX_I INT_MAX      // 1e9
#define MIN_I INT_MIN      //-1e9
#define MAX_UI UINT_MAX    // 1e9
#define MAX_LL LLONG_MAX   // 1e18
#define MIN_LL LLONG_MIN   //-1e18
#define MAX_ULL ULLONG_MAX // 1e19
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<char, char> PCC;
typedef pair<ll, ll> PLL;
typedef pair<char, int> PCI;
typedef pair<int, char> PIC;
typedef pair<ll, int> PLI;
typedef pair<int, ll> PIL;
typedef pair<ll, char> PLC;
typedef pair<char, ll> PCL;

inline void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
inline void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
inline void Yay(bool b) { cout << (b ? "Yay!" : ":(") << endl; }

string s;
vector<PCC> v;
int N, Q;
int move(int pos) {
  rep(i, Q) {
    if (s[pos] == v[i].first) {
      if (v[i].second == 'L')
        --pos;
      else
        ++pos;
    }
  }
  return pos;
}

int main(void) {
  SPEEDUP
  cout << setprecision(15);
  cin >> N >> Q;
  cin >> s;
  s = " " + s + " ";
  v.resize(Q);
  rep(i, Q) cin >> v[i].first >> v[i].second;
  // 左に落ちる最大の位置
  int ls = 0, le = N + 1;
  while (le - ls > 1) {
    int lm = (ls + le) / 2;
    if (move(lm) == 0)
      ls = lm;
    else
      le = lm;
  }

  // 右に落ちる最小の位置
  int rs = 0, re = N + 1;
  while (re - rs > 1) {
    int rm = (rs + re) / 2;
    if (move(rm) == N + 1)
      re = rm;
    else
      rs = rm;
  }
  cout << N - ls - (N + 1 - re) << endl;
  return 0;
}