Problem p03165 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

#define int long long int
#define ld long double
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
#define endl "\n"

#define si set<int>
#define vi vector<int>
#define pii pair<int, int>
#define vpii vector<pii>
#define mii map<int, int>
#define que_max priority_queue<int>
#define que_min priority_queue<int, vi, greater<int>>

#define loop(i, s, e) for (int i = s; i < e; i++)
#define rloop(i, e, s) for (int i = e; i >= s; i--)
#define mset(a, f) memset(a, f, sizeof(a))

#define M 1000000007
#define sz(x) ((int)x.size())
#define all(p) p.begin(), p.end()

#define bug(...) __f(#__VA_ARGS__, __VA_ARGS__)
#define print(a)                                                               \
  for (auto x : a)                                                             \
    cout << x << " ";                                                          \
  cout << endl
#define Print(a, x, y)                                                         \
  for (int i = x; i < y; i++)                                                  \
    cout << a[i] << " ";                                                       \
  cout << endl

inline int power(int a, int b) {
  int x = 1;
  while (b) {
    if (b & 1)
      x *= a;
    a *= a;
    b >>= 1;
  }
  return x;
}

template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}

const int N = 3e5 + 7;
int dp[3005][3005];

void solve() {
  string s, t;
  cin >> s >> t;

  int n1 = s.length();
  int n2 = t.length();
  s = " " + s;
  t = " " + t;
  mset(dp, 0);
  loop(i, 1, n1 + 1) {
    loop(j, 1, n2 + 1) {
      if (s[i] == t[j]) {
        dp[i][j] = dp[i - 1][j - 1] + 1;
      } else {
        dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
      }
    }
  }
  vector<char> v;
  int x = n1, y = n2;
  while (x > 0 and y > 0) {
    if (s[x] == t[y]) {
      v.pb(s[x]);
      x--;
      y--;
    } else {
      if (dp[x][y - 1] > dp[x - 1][y])
        y = y - 1;
      else
        x = x - 1;
    }
  }
  int cnt = v.size();
  rloop(i, cnt - 1, 0) cout << v[i];

  return;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);

#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif

  cout << setprecision(9) << fixed;

  int t = 1;
  // cin >> t;
  while (t--) {
    solve();
  }

  return 0;
}

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

#define int long long int
#define ld long double
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
#define endl "\n"

#define si set<int>
#define vi vector<int>
#define pii pair<int, int>
#define vpii vector<pii>
#define mii map<int, int>
#define que_max priority_queue<int>
#define que_min priority_queue<int, vi, greater<int>>

#define loop(i, s, e) for (int i = s; i < e; i++)
#define rloop(i, e, s) for (int i = e; i >= s; i--)
#define mset(a, f) memset(a, f, sizeof(a))

#define M 1000000007
#define sz(x) ((int)x.size())
#define all(p) p.begin(), p.end()

#define bug(...) __f(#__VA_ARGS__, __VA_ARGS__)
#define print(a)                                                               \
  for (auto x : a)                                                             \
    cout << x << " ";                                                          \
  cout << endl
#define Print(a, x, y)                                                         \
  for (int i = x; i < y; i++)                                                  \
    cout << a[i] << " ";                                                       \
  cout << endl

inline int power(int a, int b) {
  int x = 1;
  while (b) {
    if (b & 1)
      x *= a;
    a *= a;
    b >>= 1;
  }
  return x;
}

template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}

const int N = 3e5 + 7;
int dp[3005][3005];

void solve() {
  string s, t;
  cin >> s >> t;

  int n1 = s.length();
  int n2 = t.length();
  s = " " + s;
  t = " " + t;
  mset(dp, 0);
  loop(i, 1, n1 + 1) {
    loop(j, 1, n2 + 1) {
      if (s[i] == t[j]) {
        dp[i][j] = dp[i - 1][j - 1] + 1;
      } else {
        dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
      }
    }
  }
  vector<char> v;
  int x = n1, y = n2;
  while (x > 0 and y > 0) {
    if (s[x] == t[y]) {
      v.pb(s[x]);
      x--;
      y--;
    } else {
      if (dp[x][y - 1] > dp[x - 1][y])
        y = y - 1;
      else
        x = x - 1;
    }
  }
  int cnt = v.size();
  rloop(i, cnt - 1, 0) cout << v[i];

  return;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);

  cout << setprecision(9) << fixed;

  int t = 1;
  // cin >> t;
  while (t--) {
    solve();
  }

  return 0;
}