Problem p03166 (C++)

Buggy submission (status: Runtime Error):

#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse2")

/*
||||||||||||||||||||||||||||||||||||||||||||||||
   |      |||         |      ||||    ||||  |   |
  | |     |   |      | |     |   |  |      |   |
 |   |    |    |    |   |    |   |  |      |   |
|||||||   |    |   |||||||   |||     |||   |||||
|     |   |   |    |     |   | |        |  |   |
|     |   |||      |     |   |  ||  ||||   |   |
||||||||||||||||||||||||||||||||||||||||||||||||

*/
using namespace std;
// #include "testlib.h"
#define ff first
#define ss second
#define mp make_pair
#define all(v) v.begin(), v.end()
#define int long long
#define ll long long
#define M 1000000007
#define inputarr(a, n)                                                         \
  for (int i = 0; i < n; ++i)                                                  \
  cin >> a[i]
#define GCD(m, n) __gcd(m, n)
#define LCM(m, n) m *(n / GCD(m, n))
#define mii map<ll, ll>
#define msi map<string, ll>
#define mis map<ll int, string>
#define rep(a, b) for (ll i = a; i < b; i++)
#define rep0(n) for (ll i = 0; i < n; i++)
#define repi(i, a, b) for (ll i = a; i < b; i++)
#define pb push_back
#define vi vector<ll>
#define mp make_pair
#define vs vector<string>
#define ppb pop_back
#define endl '\n'
#define asdf                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define r0 return 0;
#define FORD(i, a, b) for (int i = (int)(a); i >= (int)(b); --i)
#define FORE(it, c)                                                            \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); ++it)
#define inputoutput                                                            \
  freopen("input.txt", "r", stdin);                                            \
  freopen("output.txt", "w", stdout);
#define input freopen("input.txt", "r", stdin);
#define Set(a, s) 4(a, s, sizeof(a))
#define FOR repi
#define pii pair<int, int>
#define REVERSE(v) reverse(ALL(v))
#define display(x)                                                             \
  trav(a, x) cout << a << " ";                                                 \
  cout << endl
#define debug cerr << "bhau" << endl
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  std::cerr << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  std::cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}

// #define float long double
ll max(ll a, ll b) { return (a > b) ? a : b; }
int min(int a, int b) { return (a < b) ? a : b; }
vi dp(100001, 0), vis(100001, 0);
vector<vi> adj(100001);
void dfs(int v) {
  dp[v] = 1;
  vis[v] = 1;
  for (auto i : adj[v]) {
    dp[v] = max(dp[v], 1 + dp[i]);
    if (vis[i])
      continue;
    dfs(i);
    dp[v] = max(dp[v], 1 + dp[i]);
  }
}

int solve() {
  inputoutput int n, m;
  cin >> n >> m;
  rep0(m) {
    int u, v;
    cin >> u >> v;
    adj[u].pb(v);
  }
  rep(1, n + 1) {
    if (vis[i])
      continue;
    dfs(i);
  }
  // rep(1,n+1) cout<<dp[i]<<" ";
  cout << *max_element(all(dp)) - 1;

  r0
}
signed main() {

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

Fixed submission:

#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse2")

/*
||||||||||||||||||||||||||||||||||||||||||||||||
   |      |||         |      ||||    ||||  |   |
  | |     |   |      | |     |   |  |      |   |
 |   |    |    |    |   |    |   |  |      |   |
|||||||   |    |   |||||||   |||     |||   |||||
|     |   |   |    |     |   | |        |  |   |
|     |   |||      |     |   |  ||  ||||   |   |
||||||||||||||||||||||||||||||||||||||||||||||||

*/
using namespace std;
// #include "testlib.h"
#define ff first
#define ss second
#define mp make_pair
#define all(v) v.begin(), v.end()
#define int long long
#define ll long long
#define M 1000000007
#define inputarr(a, n)                                                         \
  for (int i = 0; i < n; ++i)                                                  \
  cin >> a[i]
#define GCD(m, n) __gcd(m, n)
#define LCM(m, n) m *(n / GCD(m, n))
#define mii map<ll, ll>
#define msi map<string, ll>
#define mis map<ll int, string>
#define rep(a, b) for (ll i = a; i < b; i++)
#define rep0(n) for (ll i = 0; i < n; i++)
#define repi(i, a, b) for (ll i = a; i < b; i++)
#define pb push_back
#define vi vector<ll>
#define mp make_pair
#define vs vector<string>
#define ppb pop_back
#define endl '\n'
#define asdf                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define r0 return 0;
#define FORD(i, a, b) for (int i = (int)(a); i >= (int)(b); --i)
#define FORE(it, c)                                                            \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); ++it)
#define inputoutput                                                            \
  freopen("input.txt", "r", stdin);                                            \
  freopen("output.txt", "w", stdout);
#define input freopen("input.txt", "r", stdin);
#define Set(a, s) 4(a, s, sizeof(a))
#define FOR repi
#define pii pair<int, int>
#define REVERSE(v) reverse(ALL(v))
#define display(x)                                                             \
  trav(a, x) cout << a << " ";                                                 \
  cout << endl
#define debug cerr << "bhau" << endl
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  std::cerr << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  std::cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}

// #define float long double
ll max(ll a, ll b) { return (a > b) ? a : b; }
int min(int a, int b) { return (a < b) ? a : b; }
vi dp(100001, 0), vis(100001, 0);
vector<vi> adj(100001);
void dfs(int v) {
  dp[v] = 1;
  vis[v] = 1;
  for (auto i : adj[v]) {
    dp[v] = max(dp[v], 1 + dp[i]);
    if (vis[i])
      continue;
    dfs(i);
    dp[v] = max(dp[v], 1 + dp[i]);
  }
}

int solve() { // inputoutput
  int n, m;
  cin >> n >> m;
  rep0(m) {
    int u, v;
    cin >> u >> v;
    adj[u].pb(v);
  }
  rep(1, n + 1) {
    if (vis[i])
      continue;
    dfs(i);
  }
  // rep(1,n+1) cout<<dp[i]<<" ";
  cout << *max_element(all(dp)) - 1;

  r0
}
signed main() {

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