C++ 代码

#include <iostream>
#include <cstring>

using namespace std;

const int N = 100010;

int e[N] , ne[N] , h[N] , idx;
int n , m;
int max_len = 0;
void add(int a, int b){
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx;
    idx++;
}

int dfs(int x)
{
    int ret = 0;
    for(int i = h[x] ; ~i ; i = ne[i])
    {
        int j = e[i];
        int tmp = dfs(j);
        max_len = max(max_len, tmp + ret);
        ret = max(ret, tmp);
    }
    max_len = max(max_len , ret);
    return ret + 1;
}

int main()
{
    cin >> n >> m;
    memset(h , -1 , sizeof h);
    for(int i = 2 ; i <= n + m ; i++)
    {
        int j;
        cin >> j;
        add(j , i);
    }
    dfs(1);
    cout << max_len << endl;
}