Submission #676674

#	Time	Username	Problem	Language	Result	Execution time	Memory
676674		QwertyPi	Islands (IOI08_islands)	C++14	70 / 100	335 ms	131072 KiB

islands

#include <bits/stdc++.h>
#define int long long
#define fi first
#define se second
using namespace std;

const int N = 1e6 + 11;
vector<pair<int, int>> G[N];
int p[N], w[N], de[N], anc[N][20], dp[N];

bool vis[N], cyc[N];

struct edge{
	int u, v, w;
};

vector<edge> extra;
void dfs(int id, int v, int pa = -1){
	vis[v] = true;
	for(auto i : G[v]){
		if(!vis[i.fi]){
			de[i.fi] = de[v] + 1;
			p[i.fi] = v; anc[i.fi][0] = p[i.fi];
			for(int j = 1; j < 20; j++) anc[i.fi][j] = anc[anc[i.fi][j - 1]][j - 1];
			dfs(id, i.fi, v);
			w[i.fi] = i.se;
		}else if(i.fi != pa){
			extra[id] = {v, i.fi, i.se};
		}
	}
}

int kth_anc(int u, int k){
	for(int j = 19; j >= 0; j--){
		if(k & (1 << j)) u = anc[u][j];
	}
	return u;
}

int lca(int u, int v){
	if(de[u] < de[v]) swap(u, v);
	u = kth_anc(u, de[u] - de[v]);
	for(int i = 19; i >= 0; i--){
		if(anc[u][i] != anc[v][i])
			u = anc[u][i], v = anc[v][i];
	}
	return u == v ? u : p[u];
}

int ans[N];
void dfs_dp(int id, int v, int pa = -1){
	vector<int> dis;
	for(auto i : G[v]){
		if(!cyc[i.fi] && i.fi != pa){
			dfs_dp(id, i.fi, v);
			dis.push_back(dp[i.fi] + i.se);
		}
	}
	sort(dis.begin(), dis.end());
	if(dis.size() >= 2) ans[id] = max(ans[id], dis.back() + dis[dis.size() - 2]);
	if(dis.size()) dp[v] = dis.back(), ans[id] = max(ans[id], dis.back());
}

void solve(int id, vector<int> DP, vector<int> W){
	int n = W.size();
	vector<int> S(n * 2 + 1);
	S[0] = 0;
	for(int i = 0; i < n; i++){
		S[i + 1] = S[i] + W[i];
	}
	for(int i = 0; i < n; i++){
		S[n + i + 1] = S[n + i] + W[i];
	}
	priority_queue<int> pq, _pq;
	for(int i = 0; i < n; i++){
		pq.push(S[i] + DP[i]);
	}
	for(int i = 0; i < n; i++){
		_pq.push(S[i] + DP[i]);
		while(pq.size() && _pq.size() && pq.top() == _pq.top()) pq.pop(), _pq.pop();
		ans[id] = max(ans[id], DP[i] - S[i] + pq.top());
		pq.push(S[i + n] + DP[i]);
	}
}

int32_t main(){
	cin.tie(0); cout.tie(0)->sync_with_stdio(false);
	int n; cin >> n;
	for(int i = 1; i <= n; i++){
		int v, _w; cin >> v >> _w;
		G[i].push_back({v, _w});
		G[v].push_back({i, _w});
	}
	
	vector<int> roots;
	for(int i = 1; i <= n; i++){
		if(!vis[i]){
			extra.resize(extra.size() + 1);
			dfs(roots.size(), i);
			roots.push_back(i);
		}
	}
	
	int CC = roots.size();
	for(int i = 0; i < CC; i++){
		vector<pair<int, int>> cyc_L, cyc_R;
		int x = extra[i].u, y = extra[i].v;
		int l = lca(x, y);
		vector<int> cyc_v;
		while(x != l){
			cyc_v.push_back(x);
			cyc[x] = true;
			cyc_L.push_back({x, w[x]});
			x = p[x];
		}
		while(y != l){
			cyc_v.push_back(y);
			cyc[y] = true;
			cyc_R.push_back({y, w[y]});
			y = p[y];
		}
		cyc_v.push_back(l);
		cyc[l] = true;
		for(auto v : cyc_v){
			dfs_dp(i, v);
		}
		vector<int> V, W, DP;
		for(auto i : cyc_L){
			V.push_back(i.fi);
			DP.push_back(dp[i.fi]);
			W.push_back(i.se);
		}
		V.push_back(l);
		DP.push_back(dp[l]);
		for(int i = (int) cyc_R.size() - 1; i >= 0; i--){
			V.push_back(cyc_R[i].fi);
			DP.push_back(dp[cyc_R[i].fi]);
			W.push_back(cyc_R[i].se); 
		}
		W.push_back(extra[i].w);
		solve(i, DP, W);
	}
	cout << accumulate(ans, ans + CC, 0LL) << endl;
}

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10