Problem p03081 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (int i = (int)(0); i < (int)(n); ++i)
#define reps(i, n) for (int i = (int)(1); i <= (int)(n); ++i)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rreps(i, n) for (int i = ((int)(n)); i > 0; i--)
#define irep(i, m, n) for (int i = (int)(m); i < (int)(n); ++i)
#define ireps(i, m, n) for (int i = (int)(m); i <= (int)(n); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v + n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cout(d) cout << d << endl;
#define coutd(d) cout << std::setprecision(10) << d << endl;
#define cinline(n) getline(cin, n);
#define replace_all(s, b, a) replace(s.begin(), s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) int(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

const int INF = 1e9;
const int MOD = 1e9 + 7;
const ll LINF = 1e18;

ll n, q;
string s;
vector<char> t, d;

bool isOkL(ll mid) {
  ll pos = mid;
  rep(i, q) {
    if (s[pos] == t[i]) {
      if (d[i] == 'L') {
        pos--;
        if (pos < 0)
          return true;
      } else {
        pos++;
        if (pos >= n)
          return false;
      }
    }
  }
  return false;
}

bool isOkR(ll mid) {
  ll pos = mid;
  rep(i, q) {
    if (s[pos] == t[i]) {
      if (d[i] == 'R') {
        pos++;
        if (pos >= n)
          return true;
      } else {
        pos--;
        if (pos < 0)
          return false;
      }
    }
  }
  return false;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> q >> s;
  t.resize(n), d.resize(n);
  rep(i, q) cin >> t[i] >> d[i];

  ll ans = 0;
  ll ok = -1, ng = n + 1;
  while (abs(ok - ng) > 1) {
    ll m = (ok + ng) / 2;
    if (isOkL(m))
      ok = m;
    else
      ng = m;
  }
  ans = ok + 1;

  ok = n, ng = -1;
  while (abs(ok - ng) > 1) {
    ll m = (ok + ng) / 2;
    if (isOkR(m))
      ok = m;
    else
      ng = m;
  }
  ans += n - ok;
  ans = n - ans;
  chmin(ans, n);
  cout << ans << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (int i = (int)(0); i < (int)(n); ++i)
#define reps(i, n) for (int i = (int)(1); i <= (int)(n); ++i)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rreps(i, n) for (int i = ((int)(n)); i > 0; i--)
#define irep(i, m, n) for (int i = (int)(m); i < (int)(n); ++i)
#define ireps(i, m, n) for (int i = (int)(m); i <= (int)(n); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v + n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cout(d) cout << d << endl;
#define coutd(d) cout << std::setprecision(10) << d << endl;
#define cinline(n) getline(cin, n);
#define replace_all(s, b, a) replace(s.begin(), s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) int(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

const int INF = 1e9;
const int MOD = 1e9 + 7;
const ll LINF = 1e18;

ll n, q;
string s;
vector<char> t, d;

bool isOkL(ll mid) {
  ll pos = mid;
  rep(i, q) {
    if (s[pos] == t[i]) {
      if (d[i] == 'L') {
        pos--;
        if (pos < 0)
          return true;
      } else {
        pos++;
        if (pos >= n)
          return false;
      }
    }
  }
  return false;
}

bool isOkR(ll mid) {
  ll pos = mid;
  rep(i, q) {
    if (s[pos] == t[i]) {
      if (d[i] == 'R') {
        pos++;
        if (pos >= n)
          return true;
      } else {
        pos--;
        if (pos < 0)
          return false;
      }
    }
  }
  return false;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> q >> s;
  t.resize(q), d.resize(q);
  rep(i, q) cin >> t[i] >> d[i];

  ll ans = 0;
  ll ok = -1, ng = n + 1;
  while (abs(ok - ng) > 1) {
    ll m = (ok + ng) / 2;
    if (isOkL(m))
      ok = m;
    else
      ng = m;
  }
  ans = ok + 1;

  ok = n, ng = -1;
  while (abs(ok - ng) > 1) {
    ll m = (ok + ng) / 2;
    if (isOkR(m))
      ok = m;
    else
      ng = m;
  }
  ans += n - ok;
  ans = n - ans;
  chmin(ans, n);
  cout << ans << endl;
}