Language: C++

#include <iostream>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <queue>
#include <stack>
#include <functional>

using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<ll,ll> P;
typedef vector<P> vpl;
#define rep(i,n) for(ll i=0; i<(n); i++)
#define REP(i,a,b) for(ll i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = 1<<30;
const ll linf = 1LL<<62;
const int mod = 1e9+7;
const int MAX = 510000;
const int V = 100005;
ll dy[8] = {1,0,-1,0,1,-1,1,-1};
ll dx[8] = {0,1,0,-1,1,-1,-1,1};
const double pi = acos(-1);
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){cout << a << " " << b << endl;}
#define INT_MAX 1e9+7

int main(){
    ll n; cin >> n;
    vl a(n);
    vvl G(n);
    REP(i,1,n){
        cin >> a[i];
        a[i]--;
        G[a[i]].push_back(i);
    }
    vl d(n,inf);
    d[0] = 0;
    queue<ll> q;
    q.push(0);
    while(!q.empty()){
        ll u = q.front(); q.pop();
        for(auto v : G[u]){
            d[v] = d[u] + 1;
            q.push(v);
        }
    }
    ll ans = 0;
    rep(i,n){
        if(d[i]!=inf) ans = max(ans,d[i] + G[i].size());
    }
    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:57:32: error: no matching function for call to 'max(ll&, long long unsigned int)'
   57 |         if(d[i]!=inf) ans = max(ans,d[i] + G[i].size());
      |                             ~~~^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:57:32: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'long long unsigned int')
   57 |         if(d[i]!=inf) ans = max(ans,d[i] + G[i].size());
      |                             ~~~^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:7:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:57:32: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   57 |         if(d[i]!=inf) ans = max(ans,d[i] + G[i].size());
      |                             ~~~^~~~~~~~~~~~~~~~~~~~~~~~