Submission #59215

#	Time	Username	Problem	Language	Result	Execution time	Memory
59215		gnoor	Islands (IOI08_islands)	C++17	12 / 100	1099 ms	132096 KiB

islands

#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;

struct edge {
	int to,wgt;
	int id;
};

vector<edge> pth[1000100];
bool visit[1000100];
bool incyc[1000100];

int cyc[2000100];
long long wgt[2000100];
long long dis[2000100];
int cn;

int dfs(int x,int p) {
	visit[x]=true;
	int ret=0;
	bool toret=false;
	for (auto i:pth[x]) {
		if (i.id==p) continue;
		if (visit[i.to]) {
			if (toret) continue;
			cyc[cn]=x;
			wgt[cn]=i.wgt;
			incyc[x]=true;
			cn++;
			ret=i.to;
			toret=true;
			continue;
		}
		int res=dfs(i.to,i.id);
		if (toret) continue;
		if (res) {
			cyc[cn]=x;
			wgt[cn]=i.wgt;
			incyc[x]=true;
			cn++;
			if (res!=x) ret=res;
			else ret=0;
			toret=true;
		}
	}
	return ret;
}

long long dmax[1000100];
long long survey(int x,int p) {
	long long res=0;
	long long mx=0;
	long long smx=0;
	long long cur;
	dmax[x]=0;
	for (auto i:pth[x]) {
		if (i.id==p) continue;
		if (incyc[i.to]) continue;
		cur=i.wgt+survey(i.to,i.id);
		if (cur>=mx) {
			smx=mx;
			mx=cur;
		} else if (cur>smx) {
			smx=cur;
		}
		res=max(res,i.wgt+cur);
		dmax[x]=max(dmax[x],dmax[i.to]);
	}
	dmax[x]=max(dmax[x],mx+smx);
	return res;
}

int main () {
	int n;
	scanf("%d",&n);
	int a,b;
	for (int i=1;i<=n;i++) {
		scanf("%d%d",&a,&b);
		pth[i].push_back(edge{a,b,i});
		pth[a].push_back(edge{i,b,i});
	}
	long long ans=0;
	for (int i=1;i<=n;i++) {
		if (visit[i]) continue;
		cn=1;
		dfs(i,0);
		cn--;
		for (int j=1;j<=cn;j++) {
			dis[j]=survey(cyc[j],0);	
			dis[j+cn]=dis[j];
			wgt[j+cn]=wgt[j];
			cyc[j+cn]=cyc[j];
		}
		wgt[0]=0;
		for (int j=1;j<=cn*2;j++) {
			wgt[j]+=wgt[j-1];
		}	
		deque<int> qq;
		qq.push_back(1);
		long long cur=0;
		for (int j=2;j<=cn*2;j++) {
			while (!qq.empty()&&qq.front()<=j-cn) qq.pop_front();
			cur=max(cur,wgt[j]+dis[j]+dis[qq.front()]-wgt[qq.front()]);
			cur=max(cur,dmax[cyc[j]]);

			while (!qq.empty()&&dis[qq.back()]-wgt[qq.back()]<=dis[j]-wgt[j]) qq.pop_back();
			qq.push_back(j);
		}
		ans+=cur;
	}
	printf("%lld\n",ans);
	return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:79:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ~~~~~^~~~~~~~~
islands.cpp:82:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d",&a,&b);
   ~~~~~^~~~~~~~~~~~~~

• Subtask 1: 12 / 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