Submission #1772574

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Source Code Expand

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

struct Edge {
	int dest, len;
};

Edge children[131075][2];

long long lim;

vector<pair<long long, long long>> g(const vector<pair<long long, long long>> &r0, const vector<pair<long long, long long>> &r1) {
	vector<pair<long long, long long>> result;
	for (auto il = r0.cbegin(), ir = r1.cbegin(); il != r0.cend() || ir != r1.cend(); ) {
		if (il != r0.cend() && (ir == r1.cend() || il->first < ir->first || (il->first == ir->first && il->second == ir->second))) {
			if (result.empty() || il->second < result.back().second)
				result.push_back(*il);
			++il;
		} else {
			if (result.empty() || ir->second < result.back().second)
				result.push_back(*ir);
			++ir;
		}
	}

	return result;
}

vector<pair<long long, long long>> f(int x) {
	if (children[x][0].dest == 0) return {{0, 0}};
	
	vector<pair<long long, long long>> ls = f(children[x][0].dest), rs = f(children[x][1].dest), result0, result1;

	auto check = [=](vector<pair<long long, long long>>::const_iterator i1, vector<pair<long long, long long>>::const_iterator i2) {
		return i1->second + i2->first <= lim - (children[x][0].len + children[x][1].len);
	};

	for (auto il = ls.cbegin(), ir = rs.cbegin(); il != ls.cend(); ++il) {
		while (ir != rs.cend() && check(il, ir)) ++ir;
		if (ir != rs.cbegin()) result0.emplace_back(il->first + children[x][0].len, (ir - 1)->second + children[x][1].len);
	}

	for (auto ir = rs.cbegin(), il = ls.cbegin(); ir != rs.cend(); ++ir) {
		while (il != ls.cend() && check(ir, il)) ++il;
		if (il != ls.cbegin()) result1.emplace_back(ir->first + children[x][1].len, (il - 1)->second + children[x][0].len);
	}

	auto result = g(result0, result1);
	// cerr << '[' << lim << ']' << ' ' << x << endl;
	// cerr << '0' << '\t';
	// for (auto p: result0) cerr << '(' << p.first << ',' << ' ' << p.second << ')' << '\t';
	// cerr << endl << '1' << '\t';
	// for (auto p: result1) cerr << '(' << p.first << ',' << ' ' << p.second << ')' << '\t';
	// cerr << endl << 'g' << '\t';
	// for (auto p: result) cerr << '(' << p.first << ',' << ' ' << p.second << ')' << '\t';
	// cerr << endl;

	return result;
}

int main() {
	int n;
	cin >> n;

	for (int i = 2; i <= n; ++i) {
		int a, v;
		cin >> a >> v;
		if (children[a][0].dest == 0) {
			children[a][0] = (Edge){i, v};
		} else {
			children[a][1] = (Edge){i, v};
		}
	}

	long long low = 0, high = 131072LL * (n - 1);
	while (low < high) {
		long long mid = (low + high) / 2;
		lim = mid;
		if (!f(1).empty()) high = mid; else low = mid + 1;
	}

	cout << low << endl;

	return 0;
}

Submission Info

Judge Result