Language: C++

////=====BIsmillahir Rahmanir Rahim =====////

/*                        ______
 _______   /\     |``\   |        |  /
    |     /  \    |__/   |____    |/
    |    / _ _\   |  \   |        |\
    |   /      \  |   \  |______  |  \

            Dept. of CSE
         Comilla University

*/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
#define fi 2*acos(0.0)
#define ee 2.71828
#define ll  long long
#define FIO ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define Node struct node
#define spc " "
#define  E  2.71828182845904523536
#define pb push_back
#define pp pop_back
#define ff first
#define ss second
#define valid(nx,ny) nx>=0 && nx<n && ny>=0 && ny<m
#define edl printf("\n")
#define infinity 1e16
#define mod 1000000007
#define cn continue
#define csprint1 printf("Case %lld: ", cs++)
#define csprint2 printf("Case %lld:\n", cs++)
#define sf(a) scanf("%lld", &a)
#define sff(a,b) scanf("%lld %lld",&a,&b)
#define sfff(a,b,c) scanf("%lld %lld %lld",&a,&b,&c)
#define sffff(a,b,c,d) scanf("%lld %lld %lld %lld",&a,&b,&c,&d)
#define all(v) v.begin(),v.end()
#define pfn(a) printf("%lld\n",a)
#define pfs(a) printf("%lld ",a)

using namespace __gnu_pbds;
using namespace std;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<pl> vpi;
typedef vector<pl> vpl;
typedef tree<pair<ll, int> , null_type, less<pair<ll, int> >, rb_tree_tag, tree_order_statistics_node_update> ost;
#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args)
{
    cerr << *it << " = " << a <<","<< spc;
    err(++it, args...);
    cout<<edl;
}
///Bit manipulation

bool checkbit(int mask,int bit){return mask & (1<<bit);}
int setbit(int mask,int bit){ return mask | (1<<bit) ; }
int clearbit(int mask,int bit){return mask & ~(1<<bit);}
int togglebit(int mask,int bit){return mask ^ (1<<bit);}
int bitno(int mask) {return (int)__builtin_popcount(mask);}

/*----------------------Graph Moves----------------*/
const int fx[]={+1,-1,+0,+0};
const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

///=====================================///
const long long maX=1e5+5;
vector<ll>ara[maX];
ll dp[maX],visit[maX];
ll dfs(ll x){
    if(visit[x])return dp[x];
    ll ans=0;
    for(auto it : ara[x]){
        ans=max(ans,dfs(it)+1);
    }
    visit[x]=1;
    return dp[x]=ans;
}
int main(){
    ll n,m;
    sff(n,m);
    ll cc=0;
    for(ll i=1;i<=m;i++){
        ll x,y;sff(x,y);
        ara[x].pb(y);
    }
    ll mx=0;
    for(ll i=1;i<=n;i++){
        ll x=dfs(i);
        mx=max(x,mx);
    }
    pfn(mx);
return 0;
}


Compiler output:
a.cc: In function 'long long int dfs(long long int)':
a.cc:81:8: error: reference to 'visit' is ambiguous
   81 |     if(visit[x])return dp[x];
      |        ^~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:80,
                 from a.cc:13:
/usr/include/c++/14/variant:1855:5: note: candidates are: 'template<class _Visitor, class ... _Variants> constexpr std::__detail::__variant::__visit_result_t<_Visitor, _Variants ...> std::visit(_Visitor&&, _Variants&& ...)'
 1855 |     visit(_Visitor&& __visitor, _Variants&&... __variants)
      |     ^~~~~
a.cc:79:12: note:                 'long long int visit [100005]'
   79 | ll dp[maX],visit[maX];
      |            ^~~~~
a.cc:86:5: error: reference to 'visit' is ambiguous
   86 |     visit[x]=1;
      |     ^~~~~
/usr/include/c++/14/variant:1855:5: note: candidates are: 'template<class _Visitor, class ... _Variants> constexpr std::__detail::__variant::__visit_result_t<_Visitor, _Variants ...> std::visit(_Visitor&&, _Variants&& ...)'
 1855 |     visit(_Visitor&& __visitor, _Variants&&... __variants)
      |     ^~~~~
a.cc:79:12: note:                 'long long int visit [100005]'
   79 | ll dp[maX],visit[maX];
      |            ^~~~~