L2-026 小字辈 (25分)

#include <bits/stdc++.h>
#define int ll
#pragma GCC optimize(2)
using namespace std;
typedef long long ll;
const int maxn=1e5+10;

int n;
vector<int > a[maxn];
int ans[maxn];
int de=1,top=0,f;

int  dfs(int x,int d){
    
    
    int num=a[x].size();
    if (num==0){
    
    
        if (de<d) de=d,top=0,ans[top++]=x;
        else if (de==d) ans[top++]=x;
    } else
        for (int i = 0; i < num; ++i)
            dfs(a[x][i],d+1);
    return 0;
}

void solve() {
    
    
    cin>>n;
    for (int i = 1; i <=n; ++i) {
    
    
        int t;
        cin>>t;
        if (t==-1) f=i;
        else a[t].push_back(i);
    }
    dfs(f,1);
    cout<<de;
    for (int i = 0; i < top; ++i) {
    
    
        cout<<(i==0?"\n":" ")<<ans[i];
    }
}

signed main() {
    
    
    //ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int _ = 1;
    //cin >> _;
    while (_--) {
    
    
        solve();
    }
    return 0;
}