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Author: BrandonTang89

Other_Tasks/CF2031_E_Penchick_and_Chloe_s_Trees.cpp

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+#pragma GCC optimize("Ofast")
+#pragma GCC optimize("unroll-loops")
+#include <bits/stdc++.h>
+using namespace std;
+
+typedef long long ll;
+typedef vector<int> vi;
+#define fast_cin()                    \
+    ios_base::sync_with_stdio(false); \
+    cin.tie(NULL);                    \
+    cout.tie(NULL);
+
+int n;
+vector<vector<int>> children;
+vector<int> memo;
+
+void dfs(int u) {
+    for (auto v : children[u]) {
+        dfs(v);
+    }
+
+    priority_queue<int, vector<int>, greater<int>> pq;  // min heap
+    int count = 0;
+    for (auto v : children[u]) {
+        pq.push(memo[v]);
+        count++;
+    }
+
+    while (count > 2) {
+        int least = pq.top();
+        pq.pop();
+        int second_least = pq.top();
+        pq.pop();
+        pq.emplace(max(least, second_least) + 1);
+        count--;
+    }
+
+    if (count == 0) {
+        memo[u] = 0;
+    } else if (count == 1) {
+        memo[u] = pq.top() + 1;
+    } else {
+        pq.pop();
+        memo[u] = pq.top() + 1;
+    }
+}
+int main() {
+    fast_cin();
+    int tc;
+    cin >> tc;
+    while (tc--) {
+        cin >> n;
+        children.assign(n, vector<int>());
+        for (int i = 1; i < n; i++) {
+            int p;
+            cin >> p;
+            p--;
+            children[p].push_back(i);
+        }
+
+        memo.assign(n, -1);
+        dfs(0);
+        cout << memo[0] << endl;
+    }
+
+    return 0;
+}