Problem p01558 (C++) — buggy submission, verdict: Memory Limit Exceeded

#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstdio>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <tuple>
#include <utility>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = 1e12;
const ll MOD = 1e9 + 7;
const ull B = 1e7 + 7;

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define rep(i, N) for (int i = 0; i < (N); i++)
#define ALL(s) (s).begin(), (s).end()
#define EQ(a, b) (abs((a) - (b)) < EPS)
#define EQV(a, b) (EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()))
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1

ll sq(ll num) { return num * num; }
ll mod_pow(ll x, ll n) {
  if (n == 0)
    return 1;
  if (n == 1)
    return x % MOD;
  ll res = sq(mod_pow(x, n / 2));
  res %= MOD;
  if (n % 2 == 1) {
    res *= x;
    res %= MOD;
  }
  return res;
}
ll mod_add(ll a, ll b) { return (a + b) % MOD; }
ll mod_sub(ll a, ll b) { return (a - b + MOD) % MOD; }
ll mod_mul(ll a, ll b) { return a * b % MOD; }

int n, m;
string s;
ull h[1000000];
ull BB[1000000];
set<ull> ss;

int main() {
  cin >> n >> m >> s;
  rep(i, n) {
    if (i == 0) {
      h[i] = s[i];
      BB[i] = 1;
    } else {
      h[i] = h[i - 1] * B + s[i];
      BB[i] = BB[i - 1] * B;
    }
  }

  string t;
  int l = 0, r = 0;
  rep(i, m) {
    cin >> t;
    if (t == "L++")
      l++;
    else if (t == "L--")
      l--;
    else if (t == "R++")
      r++;
    else
      r--;
    if (l == 0)
      ss.insert(h[r]);
    else
      ss.insert(h[r] - h[l - 1] * BB[r - (l - 1)]);
  }
  cout << ss.size() << endl;
}


Error: MLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstdio>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <tuple>
#include <utility>
#include <vector>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = 1e12;
const ll MOD = 1e9 + 7;

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define rep(i, N) for (int i = 0; i < (N); i++)
#define ALL(s) (s).begin(), (s).end()
#define EQ(a, b) (abs((a) - (b)) < EPS)
#define EQV(a, b) (EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()))
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1

ll sq(ll num) { return num * num; }
ll mod_pow(ll x, ll n) {
  if (n == 0)
    return 1;
  if (n == 1)
    return x % MOD;
  ll res = sq(mod_pow(x, n / 2));
  res %= MOD;
  if (n % 2 == 1) {
    res *= x;
    res %= MOD;
  }
  return res;
}
ll mod_add(ll a, ll b) { return (a + b) % MOD; }
ll mod_sub(ll a, ll b) { return (a - b + MOD) % MOD; }
ll mod_mul(ll a, ll b) { return a * b % MOD; }

int n, m;
string s;
set<string> ss;

int main() {
  cin >> n >> m >> s;
  string t;
  int l = 0, r = 0;
  rep(i, m) {
    cin >> t;
    if (t == "L++")
      l++;
    else if (t == "L--")
      l--;
    else if (t == "R++")
      r++;
    else
      r--;
    ss.insert(s.substr(l, r - l + 1));
  }
  cout << ss.size() << endl;
}