Problem p00451 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
// #define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rrep2(i, a, b) for (int i = (a)-1; i >= b; i--)
#define chmin(a, b) (a) = min((a), (b));
#define chmax(a, b) (a) = max((a), (b));
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define printV(v)                                                              \\
  cout << (#v) << ":";                                                         \\
  for (auto(x) : (v)) {                                                        \\
    cout << " " << (x);                                                        \\
  }                                                                            \\
  cout << endl;
#define printVS(vs)                                                            \\
  cout << (#vs) << ":" << endl;                                                \\
  for (auto(s) : (vs)) {                                                       \\
    cout << (s) << endl;                                                       \\
  }
#define printVV(vv)                                                            \\
  cout << (#vv) << ":" << endl;                                                \\
  for (auto(v) : (vv)) {                                                       \\
    for (auto(x) : (v)) {                                                      \\
      cout << " " << (x);                                                      \\
    }                                                                          \\
    cout << endl;                                                              \\
  }
#define printP(p) cout << (#p) << (p).first << " " << (p).second << endl;
#define printVP(vp)                                                            \\
  cout << (#vp) << ":" << endl;                                                \\
  for (auto(p) : (vp)) {                                                       \\
    cout << (p).first << " " << (p).second << endl;                            \\
  }

inline void output() { cout << endl; }
template <typename First, typename... Rest>
inline void output(const First &first, const Rest &...rest) {
  cout << first << " ";
  output(rest...);
}

using ll = long long;
using Pii = pair<int, int>;
using TUPLE = tuple<int, int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
const int inf = 1e9;
const int mod = 1e9 + 7;
using Graph = vector<vector<int>>;

string s, t;
int n, m;
int dp[4001][4001];

signed main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  while (cin >> s >> t) {
    n = s.size();
    m = t.size();
    int ans = 0;
    rep(i, n) {
      rep(j, m) {
        if (i == 0 || j == 0)
          dp[i][j] = 0;
        if (s[i] == t[j]) {
          dp[i + 1][j + 1] = dp[i][j] + 1;
          chmax(ans, dp[i + 1][j + 1]);
        } else {
          dp[i + 1][j + 1] = 0;
        }
      }
    }
    cout << ans << endl;
  }
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
// #define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rrep2(i, a, b) for (int i = (a)-1; i >= b; i--)
#define chmin(a, b) (a) = min((a), (b));
#define chmax(a, b) (a) = max((a), (b));
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define printV(v)                                                              \\
  cout << (#v) << ":";                                                         \\
  for (auto(x) : (v)) {                                                        \\
    cout << " " << (x);                                                        \\
  }                                                                            \\
  cout << endl;
#define printVS(vs)                                                            \\
  cout << (#vs) << ":" << endl;                                                \\
  for (auto(s) : (vs)) {                                                       \\
    cout << (s) << endl;                                                       \\
  }
#define printVV(vv)                                                            \\
  cout << (#vv) << ":" << endl;                                                \\
  for (auto(v) : (vv)) {                                                       \\
    for (auto(x) : (v)) {                                                      \\
      cout << " " << (x);                                                      \\
    }                                                                          \\
    cout << endl;                                                              \\
  }
#define printP(p) cout << (#p) << (p).first << " " << (p).second << endl;
#define printVP(vp)                                                            \\
  cout << (#vp) << ":" << endl;                                                \\
  for (auto(p) : (vp)) {                                                       \\
    cout << (p).first << " " << (p).second << endl;                            \\
  }

inline void output() { cout << endl; }
template <typename First, typename... Rest>
inline void output(const First &first, const Rest &...rest) {
  cout << first << " ";
  output(rest...);
}

using ll = long long;
using Pii = pair<int, int>;
using TUPLE = tuple<int, int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
const int inf = 1e9;
const int mod = 1e9 + 7;
using Graph = vector<vector<int>>;

string s, t;
int n, m;
int dp[4000][4000];

signed main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  while (cin >> s >> t) {
    n = s.size();
    m = t.size();
    int ans = 0;
    rep(i, n) {
      rep(j, m) {
        if (s[i] == t[j]) {
          dp[i + 1][j + 1] = dp[i][j] + 1;
          chmax(ans, dp[i + 1][j + 1]);
        } else {
          dp[i][j] = 0;
        }
      }
    }
    cout << ans << endl;
  }
}