Problem p02913 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define loop(it, v) for (auto it = v.begin(); it != v.end(); it++)
#define cont(i, x) for (int i = head[x]; i; i = e[i].nxt)
#define clr(a) memset(a, 0, sizeof(a))
#define ass(a, sum) memset(a, sum, sizeof(a))
#define lowbit(x) (x & -x)
#define all(x) x.begin(), x.end()
#define SC(t, x) static_cast<t>(x)
#define ub upper_bound
#define lb lower_bound
#define pqueue priority_queue
#define mp make_pair
#define pb push_back
#define pof pop_front
#define pob pop_back
#define fi first
#define se second
#define y1 y1_
#define Pi acos(-1.0)
#define iv inline void
#define enter cout << endl
#define siz(x) ((int)x.size())
#define file(x) freopen(x ".in", "r", stdin), freopen(x ".out", "w", stdout)
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;
typedef pair<int, pii> tri;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<vi> vvi;
typedef vector<string> vst;
typedef queue<int> qi;
typedef queue<pii> qii;
typedef set<int> si;
typedef map<int, int> mii;
typedef map<string, int> msi;
const int N = 5010;
const int INF = 0x3f3f3f3f;
const int iinf = 1 << 30;
const ll linf = 2e18;
const int mod = 1000000007;
const double eps = 1e-7;
void douout(double x) { printf("%lf\n", x + 0.0000000001); }
template <class T> void print(T a) {
  cout << a << endl;
  exit(0);
}
template <class T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}
template <class T> void Tmin(T &a, T &b, T &c) { return min(a, min(b, c)); }
template <class T> void Tmax(T &a, T &b, T &c) { return max(a, max(b, c)); }
void add(int &a, int b) { a = a + b < mod ? a + b : a + b - mod; }
void sub(int &a, int b) { a = (a - b + mod) % mod; }
void mul(int &a, int b) { a = (ll)a * b % mod; }
int addv(int a, int b) { return (a += b) >= mod ? a -= mod : a; }
int subv(int a, int b) { return (a -= b) < 0 ? a += mod : a; }
int mulv(int a, int b) { return (ll)a * b % mod; }
int read() {
  int f = 1, x = 0;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int pw(int a, int b) {
  int s = 1;
  for (; b; b >>= 1, a = (ll)a * a % mod)
    if (b & 1)
      s = (ll)s * a % mod;
  return s;
}

int n, ans;
string s;
int g[N][N];

signed main() {
  scanf("%d", &n);
  cin >> s;
  s = ' ' + s;
  rep(i, 1, n) rep(j, i + 1, n) if (s[i] == s[j]) { g[i][j] = g[j][i] = 1; }
  rep(i, 1, n) rep(j, i + 1, n) if (g[i][j]) {
    int len = 0;
    while (i + len < j && g[i + len][j + len])
      len++;
    chmax(ans, len);
  }
  printf("%d\n", ans);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define loop(it, v) for (auto it = v.begin(); it != v.end(); it++)
#define cont(i, x) for (int i = head[x]; i; i = e[i].nxt)
#define clr(a) memset(a, 0, sizeof(a))
#define ass(a, sum) memset(a, sum, sizeof(a))
#define lowbit(x) (x & -x)
#define all(x) x.begin(), x.end()
#define SC(t, x) static_cast<t>(x)
#define ub upper_bound
#define lb lower_bound
#define pqueue priority_queue
#define mp make_pair
#define pb push_back
#define pof pop_front
#define pob pop_back
#define fi first
#define se second
#define y1 y1_
#define Pi acos(-1.0)
#define iv inline void
#define enter cout << endl
#define siz(x) ((int)x.size())
#define file(x) freopen(x ".in", "r", stdin), freopen(x ".out", "w", stdout)
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;
typedef pair<int, pii> tri;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<vi> vvi;
typedef vector<string> vst;
typedef queue<int> qi;
typedef queue<pii> qii;
typedef set<int> si;
typedef map<int, int> mii;
typedef map<string, int> msi;
const int N = 5010;
const int INF = 0x3f3f3f3f;
const int iinf = 1 << 30;
const ll linf = 2e18;
const int mod = 1000000007;
const double eps = 1e-7;
void douout(double x) { printf("%lf\n", x + 0.0000000001); }
template <class T> void print(T a) {
  cout << a << endl;
  exit(0);
}
template <class T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}
template <class T> void Tmin(T &a, T &b, T &c) { return min(a, min(b, c)); }
template <class T> void Tmax(T &a, T &b, T &c) { return max(a, max(b, c)); }
void add(int &a, int b) { a = a + b < mod ? a + b : a + b - mod; }
void sub(int &a, int b) { a = (a - b + mod) % mod; }
void mul(int &a, int b) { a = (ll)a * b % mod; }
int addv(int a, int b) { return (a += b) >= mod ? a -= mod : a; }
int subv(int a, int b) { return (a -= b) < 0 ? a += mod : a; }
int mulv(int a, int b) { return (ll)a * b % mod; }
int read() {
  int f = 1, x = 0;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int pw(int a, int b) {
  int s = 1;
  for (; b; b >>= 1, a = (ll)a * a % mod)
    if (b & 1)
      s = (ll)s * a % mod;
  return s;
}

int n, ans;
string s;
int g[N][N];

signed main() {
  scanf("%d", &n);
  cin >> s;
  s = ' ' + s;
  rep(i, 1, n) rep(j, i + 1, n) if (s[i] == s[j]) { g[i][j] = g[j][i] = 1; }
  rep(i, 1, n) rep(j, i + 1, n) if (g[i][j]) {
    int len = 0;
    while (i + len < j && g[i + len][j + len])
      g[i + len][j + len] = 0, len++;
    chmax(ans, len);
  }
  printf("%d\n", ans);
  return 0;
}