Problem p03166 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// #include <boost/multiprecision/cpp_ll.hpp>
// typedef boost::multiprecision::cpp_ll ll;
typedef long double dd;
#define i_7 (ll)(1E9 + 7)
// #define i_7 998244353
#define i_5 i_7 - 2
ll mod(ll a) {
  ll c = a % i_7;
  if (c >= 0)
    return c;
  return c + i_7;
}
typedef pair<ll, ll> l_l;
ll inf = (ll)1E16;
#define rep(i, l, r) for (ll i = l; i <= r; i++)
#define pb push_back
ll max(ll a, ll b) {
  if (a < b)
    return b;
  else
    return a;
}
ll min(ll a, ll b) {
  if (a > b)
    return b;
  else
    return a;
}
void Max(ll &pos, ll val) { pos = max(pos, val); } // Max(dp[n],dp[n-1]);
void Min(ll &pos, ll val) { pos = min(pos, val); }
void Add(ll &pos, ll val) { pos = mod(pos + val); }
dd EPS = 1E-9;
string alp = "abcdefghijklmnopqrstuvwxyz";
#define endl "\n"
#define fastio                                                                 \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0);

ll memo[100001];
vector<ll> v[100001];

ll hoge(ll i) {
  if (memo[i] != 0) {
    return memo[i];
  }
  if (v[i].size() == 0) {
    return 0;
  }
  ll ans = 0;
  rep(j, 0, v[i].size() - 1) { ans = max(ans, hoge(v[i][j]) + 1); }
  return ans;
}

int main() {
  fastio ll n, m;
  cin >> n >> m;
  ll x, y;
  rep(i, 0, m - 1) {
    cin >> x >> y;
    v[x].pb(y);
  }
  ll ans = 0;
  rep(i, 1, n) { ans = max(ans, hoge(i)); }
  cout << ans << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// #include <boost/multiprecision/cpp_ll.hpp>
// typedef boost::multiprecision::cpp_ll ll;
typedef long double dd;
#define i_7 (ll)(1E9 + 7)
// #define i_7 998244353
#define i_5 i_7 - 2
ll mod(ll a) {
  ll c = a % i_7;
  if (c >= 0)
    return c;
  return c + i_7;
}
typedef pair<ll, ll> l_l;
ll inf = (ll)1E16;
#define rep(i, l, r) for (ll i = l; i <= r; i++)
#define pb push_back
ll max(ll a, ll b) {
  if (a < b)
    return b;
  else
    return a;
}
ll min(ll a, ll b) {
  if (a > b)
    return b;
  else
    return a;
}
void Max(ll &pos, ll val) { pos = max(pos, val); } // Max(dp[n],dp[n-1]);
void Min(ll &pos, ll val) { pos = min(pos, val); }
void Add(ll &pos, ll val) { pos = mod(pos + val); }
dd EPS = 1E-9;
string alp = "abcdefghijklmnopqrstuvwxyz";
#define endl "\n"
#define fastio                                                                 \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0);

ll memo[100001];
vector<ll> v[100001];

ll hoge(ll i) {
  if (memo[i] != 0) {
    return memo[i];
  }
  if (v[i].size() == 0) {
    return 0;
  }
  ll ans = 0;
  rep(j, 0, v[i].size() - 1) { ans = max(ans, hoge(v[i][j]) + 1); }
  return memo[i] = ans;
}

int main() {
  fastio ll n, m;
  cin >> n >> m;
  ll x, y;
  rep(i, 0, m - 1) {
    cin >> x >> y;
    v[x].pb(y);
  }
  ll ans = 0;
  rep(i, 1, n) { ans = max(ans, hoge(i)); }
  cout << ans << endl;

  return 0;
}