Submission #265497

#	Time	Username	Problem	Language	Result	Execution time	Memory
265497		square1001	Beads and wires (APIO14_beads)	C++14	28 / 100	1050 ms	768 KiB

beads

#include <vector>
#include <iostream>
#include <algorithm>
#include <functional>
using namespace std;
const long long inf = 1LL << 40;
int main() {
	// step #1. read input
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	int N;
	cin >> N;
	vector<int> ga(N - 1), gb(N - 1); vector<long long> gw(N - 1);
	for(int i = 0; i < N - 1; ++i) {
		cin >> ga[i] >> gb[i] >> gw[i];
		--ga[i], --gb[i];
	}
	// step #2. construct a graph
	vector<int> sep(N + 1);
	for(int i = 0; i < N - 1; ++i) {
		++sep[ga[i] + 1];
		++sep[gb[i] + 1];
	}
	for(int i = 0; i < N; ++i) {
		sep[i + 1] += sep[i];
	}
	vector<int> ctr(sep);
	vector<int> to(2 * N - 2); vector<long long> cost(2 * N - 2);
	for(int i = 0; i < N - 1; ++i) {
		to[ctr[ga[i]]] = gb[i]; cost[ctr[ga[i]]++] = gw[i];
		to[ctr[gb[i]]] = ga[i]; cost[ctr[gb[i]]++] = gw[i];
	}
	// step #3. calculation
	function<pair<long long, long long>(int, int)> solve = [&](int pos, int pre) {
		// returns = (no mid-blue, one mid-blue)
		long long sumcost = 0, delta = -inf;
		for(int i = sep[pos]; i < sep[pos + 1]; ++i) {
			if(to[i] == pre) continue;
			pair<long long, long long> res = solve(to[i], pos);
			sumcost += max(res.first, res.second + cost[i]);
			delta = max(delta, cost[i] - max(res.second + cost[i] - res.first, 0LL));
		}
		return make_pair(sumcost, sumcost + delta);
	};
	long long ans = 0;
	for(int i = 0; i < N; ++i) {
		pair<long long, long long> res = solve(i, -1);
		ans = max(ans, res.first);
	}
	// step #4. print the answer
	cout << ans << endl;
	return 0;
}

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43