Submission #704306

#	Time	Username	Problem	Language	Result	Execution time	Memory
704306		jamezzz	Simurgh (IOI17_simurgh)	C++17	100 / 100	525 ms	7492 KiB

simurgh

#include "simurgh.h"
#include <bits/stdc++.h>
using namespace std;
 
#define fi first
#define se second
#define pb push_back
typedef pair<int,int> ii;
 
#define maxn 505
 
struct UFDS{
	int par[maxn],rnk[maxn];
	void init(int n){
		for(int i=0;i<n;++i)par[i]=i,rnk[i]=1;
	}
	int fp(int i){
		return (par[i]==i)?i:par[i]=fp(par[i]);
	}
	void join(int x,int y){
		x=fp(x),y=fp(y);
		if(x==y)return;
		if(rnk[x]<rnk[y])par[x]=y;
		else par[y]=x;
		if(rnk[x]==rnk[y])++rnk[x];
	}
}ufds;
 
int n,m,good[maxn*maxn],edge[maxn][maxn];
int par[maxn],depth[maxn],deg[maxn],done[maxn];
vector<int> AL[maxn];
vector<ii> EL,back_edge,tree_edge;
 
void dfs(int u){
	int far=u;
	for(int v:AL[u]){
		if(depth[v]==0){
			par[v]=u;
			depth[v]=depth[u]+1;
			dfs(v);
			tree_edge.pb({u,v});
		}
		else if(v!=par[u]&&depth[far]>depth[v])far=v;
	}
	back_edge.pb({u,far});
}
 
int count(vector<int> e){
	int num=0;
	ufds.init(n);
	vector<int> ask;
	for(int i:e){
		int u,v;
		tie(u,v)=EL[i];
		ufds.join(u,v);
		ask.pb(edge[u][v]);
	}
	for(auto[u,v]:tree_edge){
		if(ufds.fp(u)!=ufds.fp(v)){
			ufds.join(u,v);
			ask.pb(edge[u][v]);
			num+=good[edge[u][v]];
		}
	}
	return count_common_roads(ask)-num;
}
 
vector<int> find_roads(int _n,vector<int> u,vector<int> v){
	n=_n;m=u.size();
	memset(edge,-1,sizeof edge);
	memset(good,-1,sizeof good);
	for(int i=0;i<m;++i){
		AL[u[i]].pb(v[i]);
		AL[v[i]].pb(u[i]);
		edge[u[i]][v[i]]=edge[v[i]][u[i]]=i;
		EL.pb({u[i],v[i]});
	}
	
	depth[0]=1;
	dfs(0);
	
	for(auto[u,v]:back_edge){
		if(u==v)continue;
		vector<ii> edges;
		edges.pb({u,v});
		ufds.init(n);
		while(u!=v){
			edges.pb({u,par[u]});
			ufds.join(u,par[u]);
			u=par[u];
		}
		
		vector<ii> others;
		for(auto[u,v]:EL){
			if(ufds.fp(u)!=ufds.fp(v)){
				others.pb({u,v});
				ufds.join(u,v);
			}
		}
		
		vector<ii> res;
		bool have_ref=false;
		int ref_type=-1,ref_val=-1;
		for(auto[u,v]:edges){
			int id=edge[u][v];
			if(good[id]!=-1&&have_ref)continue;
			if(good[id]!=-1)have_ref=true;
			vector<int> ask;
			for(auto[u,v]:others)ask.pb(edge[u][v]);
			for(auto[x,y]:edges){
				if(x!=u||y!=v)ask.pb(edge[x][y]);
			}
			res.pb({count_common_roads(ask),id});
			
			if(good[id]!=-1)ref_type=good[id],ref_val=res.back().fi;
		}
		if(res.size()==0)continue;
		sort(res.begin(),res.end());
		int small=res[0].fi,big=res.back().fi;
		for(auto[x,i]:res){
			if(x==ref_val)good[i]=ref_type;
			else if(x==big)good[i]=0;
			else if(x==small)good[i]=1;
		}
	}
	
	for(auto[u,v]:tree_edge){
		int id=edge[u][v];
		if(good[id]==-1)good[id]=1;
	}
	
	for(int u=0;u<n;++u){
		vector<int> tmp;
		for(int v:AL[u])tmp.pb(edge[u][v]);
		deg[u]=count(tmp);
	}
	
	while(true){
		int u=-1;
		for(int i=0;i<n;++i){
			if(done[i]==0&&deg[i]==1)u=i;
		}
		if(u==-1)break;
		vector<int> e;
		for(int v:AL[u]){
			if(!done[v])e.pb(edge[u][v]);
		}
		int lo=0,hi=e.size()-1,mid,res;
		while(lo<=hi){
			mid=(lo+hi)>>1;
			vector<int> tmp;
			for(int i=0;i<=mid;++i)tmp.pb(e[i]);
			if(count(tmp)==1)res=mid,hi=mid-1;
			else lo=mid+1;
		}
		good[e[res]]=1;
		int v=EL[e[res]].fi;
		if(u==v)v=EL[e[res]].se;
		--deg[v];
		done[u]=1;
	}
	
	vector<int> ans;
	for(int i=0;i<m;++i){
		if(good[i]==1)ans.pb(i);
	}
	assert(count_common_roads(ans)==n-1);
	return ans;
}

Compilation message (stderr)

simurgh.cpp: In function 'std::vector<int> find_roads(int, std::vector<int>, std::vector<int>)':
simurgh.cpp:156:13: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  156 |   good[e[res]]=1;
      |             ^

• Subtask 1: 13 / 13
• Subtask 2: 17 / 17
• Subtask 3: 21 / 21
• Subtask 4: 19 / 19
• Subtask 5: 30 / 30