Submission #379586

#	Time	Username	Problem	Language	Result	Execution time	Memory
379586		SavicS	Islands (IOI08_islands)	C++14	80 / 100	572 ms	131076 KiB

islands

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>

#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ff(i,a,b) for(int i=a;i<=b;i++)
#define fb(i,b,a) for(int i=b;i>=a;i--)

using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<int,ll> pii;
const int maxn = 1000005;
const int inf = 1e9 + 5;

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k)  print the k-th smallest number in os(0-based)

int n;

vector<pii> g[maxn];

int nxt[maxn];
ll cost[maxn];

int krug_sta = 0;
int krug_end = 0;

int par[maxn];
int visited[maxn];
void dfs1(int v, int p){
	par[v] = p;
	visited[v] = 1;
	for(auto c : g[v]){
		int u = c.fi;
		ll w = c.se;
		if(u == p && !(nxt[p] == v && nxt[v] == p))continue;
		if(!visited[u])dfs1(u, v);
		else{
			if(visited[u] == 1){
				krug_sta = u;
				krug_end = v;
			}
		}
	}
	visited[v] = 2;
}

ll dia = 0;
bool was[maxn];
ll dfs2(int v, ll duz){
	was[v] = 1;
	ll best = duz;
	for(auto c : g[v]){
		int u = c.fi;
		ll w = c.se;
		if(!was[u]){
			ll dist = dfs2(u, duz + w);
			dia = max(dia, dist + best - 2 * duz);
			best = max(best, dist);
		}
	}		
	return best;
}

ll rez = 0;
ll pref[maxn];
ll sta[maxn];
void Solve(int x){
	dia = 0;
	dfs1(x, -1);
	
	vector<int> cycle;
	for(int i = krug_end;i != krug_sta; i = par[i]){
		cycle.pb(i);	
	}
	cycle.pb(krug_sta);
	
	vector<pii> krug;
	ff(i,1,sz(cycle) - 1){
		int a = cycle[i - 1];
		int b = cycle[i];
		ll w = (nxt[a] == b ? cost[a] : cost[b]);
		krug.pb({a, w});		
	}
	ll w = (nxt[cycle.back()] == cycle[0] ? cost[cycle.back()] : cost[cycle[0]]);
	krug.pb({cycle.back(), w});
	
	for(auto c : krug)was[c.fi] = 1;
	ff(i,0,sz(krug) - 1)sta[i] = dfs2(krug[i].fi, 0);
	
	int len = sz(krug);
	pref[0] = 0;
	ff(i,0,len - 1)pref[i + 1] = pref[i] + krug[i].se;
	
	ll zbir = pref[len];
	ll mn = -sta[0];
	ll mx = sta[0];
	ll najv = 0;
	ff(i,1,len - 1){
		najv = max(najv, pref[i] + sta[i] - mn);
		najv = max(najv, zbir + sta[i] - pref[i] + mx);
		mn = min(mn, pref[i] - sta[i]);
		mx = max(mx, pref[i] + sta[i]);
	}
	rez += max(najv, dia);
}

int main()
{
    ios::sync_with_stdio(false);
    cout.tie(nullptr);
    cin.tie(nullptr);
	cin >> n;
	ff(i,1,n){
		int a;
		ll b;
		cin >> a >> b;
		g[i].pb({a, b});
		g[a].pb({i, b});
		nxt[i] = a;
		cost[i] = b;
	}
	ff(i,1,n){
		if(!visited[i]){
			Solve(i);
		}
	}
	cout << rez << endl;
    return 0;
}
/**

7
3 8
7 2
4 2
1 4
1 9
3 4
2 3 


// probati bojenje sahovski ili slicno

**/

Compilation message (stderr)

islands.cpp: In function 'void dfs1(int, int)':
islands.cpp:44:6: warning: unused variable 'w' [-Wunused-variable]
   44 |   ll w = c.se;
      |      ^

• 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: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10