Problem p00451 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cassert>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

#define REP(i, m, n) for (int i = m; i < n; i++)
#define rep(i, n) for (int i = 0; i < n; i++)
#define rp(i, c) rep(i, (int)c.size())
#define fr(i, c)                                                               \
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define mp make_pair
#define pb push_back
#define all(c) (c).begin(), (c).end()
#define rall(u) (u).rbegin(), (u).rend()
#define dbg(x) cerr << #x << " = " << (x) << endl
#define v_delete(a, b) (a).erase(remove((a).begin(), (a).end(), b), (a).end())
#define v_unique(a) (a).erase(unique((a).begin(), (a).end()), (a).end())
#define VV(T) vector<vector<T>>
#define init(a, b) memset((a), (b), sizeof((a)))

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
const int inf = 1 << 28;
const double EPS = 1e-9;
const long long INF = 100001000010000100ll;

template <class T> int SIZE(T a) { return a.size(); }
template <class T> string IntToString(T num) {
  string res;
  stringstream ss;
  ss << num;
  return ss.str();
}
template <class T> T StringToInt(string str) {
  T res = 0;
  for (int i = 0; i < SIZE(str); i++)
    res = (res * 10 + str[i] - '0');
  return res;
}
template <class T> T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

template <class T> void input(T &a, int n) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
template <class T> void input(T *a, int n) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
typedef pair<int, int> pii;

string L, R;

int dp[4000 + 10][4000 + 10];

int main() {
  while (cin >> L >> R) {
    memset(dp, 0, sizeof(dp));
    int ans = 0;
    rp(i, R) {
      rp(j, L) {
        if (R[i] == L[j]) {
          dp[i][j] = dp[i - 1][j - 1] + 1;
        } else {
          dp[i][j] = 0;
        }
        ans = max(ans, dp[i][j]);
      }
    }
    cout << ans << endl;
  }

  return 0;
}

Fixed submission:
#include <algorithm>
#include <cassert>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

#define REP(i, m, n) for (int i = m; i < n; i++)
#define rep(i, n) for (int i = 0; i < n; i++)
#define rp(i, c) rep(i, (int)c.size())
#define fr(i, c)                                                               \
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define mp make_pair
#define pb push_back
#define all(c) (c).begin(), (c).end()
#define rall(u) (u).rbegin(), (u).rend()
#define dbg(x) cerr << #x << " = " << (x) << endl
#define v_delete(a, b) (a).erase(remove((a).begin(), (a).end(), b), (a).end())
#define v_unique(a) (a).erase(unique((a).begin(), (a).end()), (a).end())
#define VV(T) vector<vector<T>>
#define init(a, b) memset((a), (b), sizeof((a)))

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
const int inf = 1 << 28;
const double EPS = 1e-9;
const long long INF = 100001000010000100ll;

template <class T> int SIZE(T a) { return a.size(); }
template <class T> string IntToString(T num) {
  string res;
  stringstream ss;
  ss << num;
  return ss.str();
}
template <class T> T StringToInt(string str) {
  T res = 0;
  for (int i = 0; i < SIZE(str); i++)
    res = (res * 10 + str[i] - '0');
  return res;
}
template <class T> T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

template <class T> void input(T &a, int n) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
template <class T> void input(T *a, int n) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
typedef pair<int, int> pii;

string L, R;

int dp[4000 + 10][4000 + 10];

int main() {
  while (cin >> L >> R) {
    memset(dp, 0, sizeof(dp));
    int ans = 0;
    rp(i, R) {
      rp(j, L) {
        if (R[i] == L[j]) {
          if (i > 0 && j > 0) {
            dp[i][j] = dp[i - 1][j - 1] + 1;
          } else {
            dp[i][j] = 1;
          }
        } else {
          dp[i][j] = 0;
        }
        ans = max(ans, dp[i][j]);
      }
    }
    cout << ans << endl;
  }

  return 0;
}