Submission #363143

#	Time	Username	Problem	Language	Result	Execution time	Memory
363143		shivensinha4	Beads and wires (APIO14_beads)	C++17	100 / 100	228 ms	18016 KiB

beads

#include "bits/stdc++.h"
using namespace std;
#define for_(i, s, e) for (int i = s; i < (int) e; i++)
#define for__(i, s, e) for (ll i = s; i < e; i++)
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> ii;
//#define endl '\n'

const int MXN = 2e5, INF = 1e9;
vector<array<int, 2>> dp;
vector<vector<array<int, 2>>> adj;
int n, ans = 0;

void dfs(int p, int parent, int pe=0) {
	dp[p] = {0, 0};
	int v = 0;
	for (auto i: adj[p]) if (i[0] != parent) {
		dfs(i[0], p, i[1]);
		v = max(v, -dp[i[0]][0] + dp[i[0]][1] + i[1] + pe);
		dp[p][1] += dp[i[0]][0];
	}
	dp[p][0] = dp[p][1] + (p == parent ? 0 : v);
}

void reroot(int p, int parent) {
	array<int, 2> opt = {-INF, -INF}, pre = dp[p];
	
	if (parent != p) dp[p][1] += dp[parent][0];

	for (auto i: adj[p]) {
		int temp = -dp[i[0]][0] + dp[i[0]][1] + i[1];
		if (temp >= opt[0]) {
			swap(opt[0], opt[1]);
			opt[0] = temp;
		} else if (temp > opt[1]) opt[1] = temp;
	}
	
	ans = max(ans, dp[p][1]);
	
	for (auto i: adj[p]) if (i[0] != parent) {
		dp[p][1] -= dp[i[0]][0];
		dp[p][0] = dp[p][1];
		
		int temp = -dp[i[0]][0] + dp[i[0]][1] + i[1];
		if (temp == opt[0]) dp[p][0] += max(opt[1]+i[1], 0);
		else dp[p][0] += max(opt[0]+i[1], 0);
		
		reroot(i[0], p);
		
		dp[p][1] += dp[i[0]][0];
	}
	
	dp[p] = pre;
}

int main() {
#ifdef mlocal
	freopen("test.in", "r", stdin);
#endif
	
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	
	cin >> n;
	dp.resize(n); adj.resize(n);
	for_(i, 0, n-1) {
		int a, b, w; cin >> a >> b >> w;
		a -= 1; b -= 1;
		adj[a].push_back({b, w}); adj[b].push_back({a, w});
	}
	
	dfs(0, 0, 0);
	reroot(0, 0);
	
	cout << ans << endl;
	
	
	return 0;
}

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