Submission #641747

#	Time	Username	Problem	Language	Result	Execution time	Memory
641747		jamezzz	Thousands Islands (IOI22_islands)	C++17	100 / 100	238 ms	44168 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;

#ifdef DEBUG
#define dbg(...) printf(__VA_ARGS__);
#define getchar_unlocked getchar
#else
#define dbg(...)
#endif
#define sf scanf
#define pf printf
#define fi first
#define se second
#define pb push_back
#define psf push_front
#define ppb pop_back
#define ppf pop_front
#define sz(x) (int)x.size()
#define mnto(x,y) x=min(x,(__typeof__(x))y)
#define mxto(x,y) x=max(x,(__typeof__(x))y)
#define INF 1023456789
#define LINF 1023456789123456789
#define all(x) x.begin(),x.end()
#define lb(x,v) (lower_bound(all(x),v)-x.begin())
#define ub(x,v) (upper_bound(all(x),v)-x.begin())
#define disc(x) sort(all(x));x.resize(unique(all(x))-x.begin());
typedef long long ll;
typedef long double ld;
typedef pair<int,int> ii;
typedef pair<ll,ll> pll;
typedef tuple<int,int,int> iii;
typedef tuple<int,int,int,int> iiii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
mt19937 rng(time(0));

#define maxn 200005

int mxdep[maxn],pedge[maxn],par[maxn],dep[maxn];
bool vis[maxn],onstk[maxn],down[maxn],incycle[maxn],bothcycle[maxn];
map<int,ii> edgeid[maxn];
vi ans,cyclenode[2],tocycle[2],tocycleid[2],cycleid[2];;
vii AL[maxn];

void add(vector<int> &v){
	for(int x:v)ans.pb(x);
}

void addrev(vector<int> &v){
	for(int i=sz(v)-1;i>=0;--i)ans.pb(v[i]);
}

void dfs(int u){
	vis[u]=onstk[u]=true;
	mxdep[u]=-1;
	for(auto[v,i]:AL[u]){
		if(!vis[v]){
			pedge[v]=i;
			par[v]=u;
			dep[v]=dep[u]+1;
			dfs(v);
			down[i]=true;
		}
		if(onstk[v])mxto(mxdep[u],dep[v]);
		else{
			mxto(mxdep[u],mxdep[v]);
			down[i]=true;
		}
	}
	onstk[u]=false;
}

bool getcyc(int u,vi &nodes){
	vis[u]=onstk[u]=true;
	for(auto[v,i]:AL[u]){
		if(!vis[v]){
			if(getcyc(v,nodes)){
				nodes.pb(u);
				return true;
			}
		}
		if(onstk[v]){
			nodes.pb(v),nodes.pb(u);
			return true;
		}
	}
	onstk[u]=false;
	return false;
}

variant<bool,vi> find_journey(int N,int M,vi U,vi V){
	for(int i=0;i<M;++i){
		AL[U[i]].pb({V[i],i});
		if(edgeid[U[i]].find(V[i])==edgeid[U[i]].end())edgeid[U[i]][V[i]]={i,i};
		else edgeid[U[i]][V[i]].se=i;
	}
	dfs(0);
	for(int rt=0;rt<N;++rt){
		vi goodedge;
		for(auto[x,i]:AL[rt]){
			if(down[i]&&mxdep[x]>=dep[rt])goodedge.pb(x);
		}
		if(sz(goodedge)<2)continue;
		vi pathtort;
		int tmp=rt;
		while(tmp){
			pathtort.pb(pedge[tmp]);
			tmp=U[pedge[tmp]];
		}
		reverse(all(pathtort));
		add(pathtort);
		for(int i=0;i<2;++i){
			int x=goodedge[i];
			memset(vis,false,sizeof vis);
			memset(onstk,false,sizeof onstk);
			for(int x:pathtort)vis[U[x]]=vis[V[x]]=true;
			vis[rt]=onstk[rt]=true;
			vi nodes;
			getcyc(x,nodes);
			nodes.pb(rt);
			while(true){
				tocycle[i].pb(nodes.back());
				if(nodes.back()!=nodes[0])nodes.ppb();
				else break;
			}
			reverse(all(nodes));
			swap(nodes,cyclenode[i]);
		}
		
		int type=0;
		for(int i:cyclenode[0])incycle[i]=true;
		for(int i:cyclenode[1]){
			if(incycle[i]){
				bothcycle[i]=true;
				if(i!=rt)type=1;
			}
		}
		for(int x=0;x<2;++x){
			for(int i=0;i<sz(tocycle[x])-1;++i){
				int u=tocycle[x][i],v=tocycle[x][i+1];
				tocycleid[x].pb(edgeid[u][v].fi);
				swap(edgeid[u][v].fi,edgeid[u][v].se);
			}
			for(int i=0;i<sz(cyclenode[x])-1;++i){
				int u=cyclenode[x][i],v=cyclenode[x][i+1];
				cycleid[x].pb(edgeid[u][v].fi);
				swap(edgeid[u][v].fi,edgeid[u][v].se);
			}
		}
		if(type==0){//disjoint cycle
			for(int x=0;x<2;++x){
				add(tocycleid[x]);
				add(cycleid[x]);
				addrev(tocycleid[x]);
			}
			for(int x=0;x<2;++x){
				add(tocycleid[x]);
				addrev(cycleid[x]);
				addrev(tocycleid[x]);
			}
		}
		else{//overlapping cycle
			add(tocycleid[0]);
			add(cycleid[0]);
			addrev(tocycleid[0]);
			add(tocycleid[1]);
			vi added;
			for(int i:cycleid[1]){
				int u=U[i],v=V[i];
				if(u!=rt&&bothcycle[u]){
					int start=-1;
					for(int j=0;j<sz(cycleid[0]);++j){
						int id=cycleid[0][j];
						int u2=U[id],v2=V[id];
						if(v2==u)start=j;
					}
					for(int j=start;j>=0;--j)ans.pb(cycleid[0][j]);
					for(int j=sz(cycleid[0])-1;j>start;--j)ans.pb(cycleid[0][j]);
					break;
				}
				ans.pb(i);
				added.pb(i);
			}
			addrev(added);
			addrev(tocycleid[1]);
		}
		addrev(pathtort);
		return ans;
	}
	return false;
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, vi, vi)':
islands.cpp:176:11: warning: unused variable 'u2' [-Wunused-variable]
  176 |       int u2=U[id],v2=V[id];
      |           ^~
islands.cpp:171:16: warning: unused variable 'v' [-Wunused-variable]
  171 |     int u=U[i],v=V[i];
      |                ^

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 21 / 21
• Subtask 4: 24 / 24
• Subtask 5: 45 / 45