Problem p00461 (C++) — buggy submission, verdict: Time Limit Exceeded

/* {{{ Shinobu kawaii */
/*
  ______   __        _                  __
.' ____ \\ [  |      (_)                [  |
| (___ \\_| | |--.   __   _ .--.   .--.  | |.--.   __   _
 _.____`.  | .-. | [  | [ `.-. |/ .'`\\ \\| '/'`\\ \\[  | | |
| \\____) | | | | |  | |  | | | || \\__. ||  \\__/ | | \\_/ |,
 \\______.'[___]|__][___][___||__]'.__.'[__;.__.'  '.__.'_/

*/
// clang-format off
/* }}} */

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

// #define int long long
struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;

/* cpp template {{{ */

/* short */
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) begin(v), end(v)
#define RALL(v) rbegin(v), rend(v)
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (ll i = (a); i < (ll)(n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (ll i = (a); i >= (ll)(n); --i)
#define DEP(i, n) DEPS(i, n, 0)

/* debug */
#define debug(x) cerr << x << " " << "(L:" << __LINE__ << ")" << '\\n';

/* alias */
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using D = double;
using P = complex<D>;
using vs = vector<string>;
template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {return y >= 0 && x >= 0 && y < H && x < W;}
inline int in() {int x; cin >> x; return x;}
inline ll IN() {ll x; cin >> x; return x;}
inline vs split(const string& t, char c) {vs v; stringstream s(t); string b; while(getline(s, b, c)) v.eb(b); return v;}
template <typename T> inline bool chmin(T& a, const T& b) {if (a > b) a = b; return a > b;}
template <typename T> inline bool chmax(T& a, const T& b) {if (a < b) a = b; return a < b;}
template <typename T> inline void print(const T& x) {cout << x << '\\n';}
template <typename T, typename S> inline void print(const vector<pair<T, S>>& v) {for (auto&& p : v) print(p);}
template <typename T> inline void print(const vector<T>& v, string s = " ") {REP(i, v.size()) cout << v[i] << (i != (ll)v.size() - 1 ? s : "\\n");}
// clang-format on
/* }}} */

signed main() {
  int n;
  while (cin >> n, n) {
    int m = in();
    string p = "I", s;
    REP(_, n) p += "OI";
    cin >> s;
    int ans = 0;
    REP(i, m) {
      if (s[i] == 'O')
        continue;
      if (2 * n + 1 + i > m)
        break;
      if (p == s.substr(i, 2 * n + 1))
        ++ans;
    }
    print(ans);
  }

  return 0;
}

Error: TLE

Fixed submission:

/* {{{ Shinobu kawaii */
/*
  ______   __        _                  __
.' ____ \\ [  |      (_)                [  |
| (___ \\_| | |--.   __   _ .--.   .--.  | |.--.   __   _
 _.____`.  | .-. | [  | [ `.-. |/ .'`\\ \\| '/'`\\ \\[  | | |
| \\____) | | | | |  | |  | | | || \\__. ||  \\__/ | | \\_/ |,
 \\______.'[___]|__][___][___||__]'.__.'[__;.__.'  '.__.'_/

*/
// clang-format off
/* }}} */

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

// #define int long long
struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;

/* cpp template {{{ */

/* short */
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) begin(v), end(v)
#define RALL(v) rbegin(v), rend(v)
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (ll i = (a); i < (ll)(n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (ll i = (a); i >= (ll)(n); --i)
#define DEP(i, n) DEPS(i, n, 0)

/* debug */
#define debug(x) cerr << x << " " << "(L:" << __LINE__ << ")" << '\\n';

/* alias */
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using D = double;
using P = complex<D>;
using vs = vector<string>;
template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {return y >= 0 && x >= 0 && y < H && x < W;}
inline int in() {int x; cin >> x; return x;}
inline ll IN() {ll x; cin >> x; return x;}
inline vs split(const string& t, char c) {vs v; stringstream s(t); string b; while(getline(s, b, c)) v.eb(b); return v;}
template <typename T> inline bool chmin(T& a, const T& b) {if (a > b) a = b; return a > b;}
template <typename T> inline bool chmax(T& a, const T& b) {if (a < b) a = b; return a < b;}
template <typename T> inline void print(const T& x) {cout << x << '\\n';}
template <typename T, typename S> inline void print(const vector<pair<T, S>>& v) {for (auto&& p : v) print(p);}
template <typename T> inline void print(const vector<T>& v, string s = " ") {REP(i, v.size()) cout << v[i] << (i != (ll)v.size() - 1 ? s : "\\n");}
// clang-format on
/* }}} */

signed main() {
  int n;
  while (cin >> n, n) {
    int m = in();
    string p = "I", s;
    REP(_, n) p += "OI";
    cin >> s;
    int ans = 0;
    for (auto pos = s.find(p); pos != string::npos; pos = s.find(p)) {
      s[pos] = 'O';
      ++ans;
    }
    print(ans);
  }

  return 0;
}