CF1739D WA

#include <assert.h>
#include <bits/stdc++.h>
using namespace std;
#define dbg(...) logger(#__VA_ARGS__, __VA_ARGS__)
template <typename... Args> void logger(string vars, Args &&... values)
{
    cerr << vars << " = ";
    string delim = "";
    (..., (cerr << delim << values, delim = ", "));
    cerr << endl;
}

template <class T> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m)); }
template <class T> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n)); }
template <class T, T init> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m, init)); }
template <class T, T init> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n, init)); }

template <class T> using mpq = priority_queue<T, vector<T>, greater<T>>;

using ll = long long;
using pii = pair<int, int>;
using vl = vector<ll>;
using vi = vector<int>;

int main(int argc, char **argv)
{
    int t;
    cin >> t;
    while (t--) {
        int n, k;
        cin >> n >> k;
        vi p(n + 1);
        vector<int> tree[200003];
        for (int i = 2; i <= n; ++i) {
            cin >> p[i];
            tree[p[i]].push_back(i);
        }
        int lb = 1, ub = 200003, cnt = ub - lb, it, step;
        int ans = 0;
        function<int(int, int, int)> dfs = [&tree, &ans, &dfs](int u, int fa, int len) {
            int unfinish = 1;
            for (auto v : tree[u]) {
                if (v == fa)
                    continue;
                int zlen = dfs(v, u, len);
                unfinish = max(zlen, unfinish);
            }
            unfinish += 1;
            if (unfinish + 1 == len)
                unfinish = 0, ans += 1;
            return unfinish == INT_MIN ? 1 : unfinish;
        };
        auto check = [&ans, &dfs](int height) {
            ans = 0;
            dfs(1, -1, height);
            return ans;
        };
        while (cnt) {
            it = lb, step = cnt / 2, it += step;
            if (check(it) > k) {
                lb = it + 1;
                cnt = cnt - (step + 1);
            } else {
                cnt = step;
            }
        }
        cout << lb << endl;
    }
    return 0;
};