Submission #120273

#	Time	Username	Problem	Language	Result	Execution time	Memory
120273		nvmdava	Islands (IOI08_islands)	C++17	18 / 100	712 ms	131072 KiB

islands

#include <bits/stdc++.h>
using namespace std;
#define N 1000001

vector<pair<int, long long> > adj[N];
bool in[N];
vector<int> s;
long long dp[N][3];
vector<int> cyc;
bool inCyc[N];

void dfs(int v, int p){
	long long b1 = 0, b2 = 0;
	for(auto xx : adj[v]){
		int x = xx.first;
		long long c = xx.second;
		
		if(inCyc[x] || p == x) continue;
		dfs(x, v);
		
		long long up;
		dp[v][0] += dp[x][2];
		up = dp[x][1] - dp[x][2] + c;
		if(b1 < up){
			b2 = b1;
			b1 = up;
		} else b2 = max(b2, up);
	}
	dp[v][1] = dp[v][0] + b1;
	dp[v][2] = dp[v][0] + b1 + b2;
}
long long ans = 0;
unordered_map<int, unordered_map<int, int> > lol; 

void solve(){
	for(int x : s){
		if(inCyc[x]) {	
			cyc.push_back(x);
			dfs(x, 0);
		}
	}
	
	long long dp[2][2][3][3];
	memset(dp, -0x3f, sizeof dp);
	dp[0][0][0][0] = ::dp[cyc[0]][0];
	dp[0][0][1][1] = ::dp[cyc[0]][1];
	dp[0][0][2][2] = ::dp[cyc[0]][2];
	
	int st = 0;
	for(int i = 1; i < cyc.size(); i++){
		st = i & 1;
		memset(dp[st], -0x3f, sizeof dp[st]);
		for(int t = 0; t <= 2; t++){
			
			for(int j = 0; j <= 2; j++){
				for(int l = 0; l <= 2; l++){
					dp[st][1][t][j] = max(dp[st][1][t][j], dp[st ^ 1][0][t][l] + ::dp[cyc[i]][j]);
					dp[st][1][t][j] = max(dp[st][1][t][j], dp[st ^ 1][1][t][l] + ::dp[cyc[i]][j]);
				}
			}
			if(i == 1 && t == 2) break;
			for(int j = 1; j <= 2; j++){
				for(int l = 0; l < 2; l++){
					if(i == 1){
						dp[st][1][t + 1][j] = max(dp[st][1][t][j], dp[st ^ 1][1][t][l] + ::dp[cyc[i]][j - 1] + lol[cyc[i]][cyc[i - 1]]);
						dp[st][0][t + 1][j] = max(dp[st][0][t][j], dp[st ^ 1][0][t][l] + ::dp[cyc[i]][j - 1] + lol[cyc[i]][cyc[i - 1]]);
					} else {				
						dp[st][1][t][j] = max(dp[st][1][t][j], dp[st ^ 1][1][t][l] + ::dp[cyc[i]][j - 1] + lol[cyc[i]][cyc[i - 1]]);
						dp[st][0][t][j] = max(dp[st][0][t][j], dp[st ^ 1][0][t][l] + ::dp[cyc[i]][j - 1] + lol[cyc[i]][cyc[i - 1]]);
					}
				}
			}
		}
	}
	long long res = 0;
	for(int i = 0; i < 3; i++){
		for(int j = 0; j < 3; j++){
			res = max(res, dp[st][0][i][j]);
			res = max(res, dp[st][1][i][j]);
		}
	}
	for(int i = 0; i < 2; i++){
		for(int j = 0; j < 2; j++){
			res = max(res, dp[st][1][i][j] + lol[cyc[0]][cyc.back()]);
		}
	}
	
	ans += res;
}

int trav(int i, int p){
	s.push_back(i);
	in[i] = 1;
	int res = 0;
	bool ok = 0;
	for(auto xx : adj[i]){
		int x = xx.first;
		if(p == x && ok == 0){
			ok = 1;	
			continue;
		}
		if(in[x]){
			res = x;
			continue;
		}
		int t = trav(x, i);
		if(res < t)res = t;
	}
	if(res) inCyc[i] = 1;
	if(res == i) return 0;
	return res;
}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int n;
	cin>>n;
	
	for(int i = 1; i <= n; i++){
		int l, e;
		cin>>e>>l;
		adj[e].push_back({i, l});
		adj[i].push_back({e, l});
		lol[e][i] = max(lol[e][i], l);
		lol[i][e] = max(lol[i][e], l);
	}
	
	for(int i = 1; i <= n; i++){
		if(in[i]) continue;
		s.clear();
		cyc.clear();		
		trav(i, 0);
		solve();
	}
	
	cout<<ans;
}

Compilation message (stderr)

islands.cpp: In function 'void solve()':
islands.cpp:50:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 1; i < cyc.size(); i++){
                 ~~^~~~~~~~~~~~

• Subtask 1: 18 / 33
• Subtask 2: 0 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10