DP on tree - 1065F Codeforces

//Make CSP great again
//You're as beautiful as the day I lost you
#include <bits/stdc++.h>
#define TASK "TESTCODE"
using namespace std;
const int N = 1e6;
vector<int> Adj[N + 1];
int n, depth[N + 1], k, dp[N + 1][3];
void read()
{
    cin >> n >> k;
    for (int i = 2; i <= n; ++ i)
    {
        int p;
        cin >> p;
        Adj[p].push_back(i);
    }
}
void DFS(int u)
{
    if (Adj[u].empty())
    {
        dp[u][0] = depth[u] - k;
        dp[u][1] = dp[u][2] = 1;
        return ;
    }
    dp[u][0] = N + 10;
    dp[u][1] = dp[u][2] = 0;
    for (int v : Adj[u])
    {
        depth[v] = depth[u] + 1;
        DFS(v);
        if (dp[v][0] <= depth[u])
        {
            dp[u][0] = min(dp[u][0], dp[v][0]);
            dp[u][1] += dp[v][1];
        }
    }
    for (int v : Adj[u])
    {
        if (dp[v][0] <= depth[u])
        {
            dp[u][2] = max(dp[u][2], dp[v][2] + dp[u][1] - dp[v][1]);
        }
        else
        {
            dp[u][2] = max(dp[u][2], dp[u][1] + dp[v][2]);
        }
    }
}
void solve()
{
    DFS(1);
    /*for (int i = 1; i <= n; ++ i)
    {
        cerr << dp[i][1] << ' ';
    }
    cerr << '\n';*/
    cout << dp[1][2];
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        //freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}