Submission #233862

#	Time	Username	Problem	Language	Result	Execution time	Memory
233862		LittleFlowers__	Network (BOI15_net)	C++17	100 / 100	1089 ms	91884 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define in ({int x=0;int c=getchar(),n=0;for(;!isdigit(c);c=getchar()) n=(c=='-');for(;isdigit(c);c=getchar()) x=x*10+c-'0';n?-x:x;})
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//mt19937 rng(1012);
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define fasty ios_base::sync_with_stdio(0),cin.tie(0);
#define forinc(a,b,c) for(int a=b,_c=c;a<=_c;++a)
#define fordec(a,b,c) for(int a=b,_c=c;a>=_c;--a)
#define forv(a,b) for(auto&a:b)
#define fi first
#define se second
#define pb push_back
#define ii pair<int,int>
#define mt make_tuple
#define all(a) a.begin(),a.end()
#define reset(f, x) memset(f, x, sizeof(f))
#define bit(x,i) ((x>>(i-1))&1)
#define on(x,i) (x|(1ll<<(i-1)))
#define off(x,i) (x&~(1<<(i-1)))
#define gg exit(0);

const int N=500010;

int n;
vector<int> val;
vector<int> ad[N],adj[N];

vector<ii> ans;

void add(int i,int j){
    adj[i].pb(j);
    adj[j].pb(i);
    ans.pb({i,j});
}

int it,top,scc;
int st[N],ed[N],co[N],w[N],tr[N];

void dfs1(int u){
    st[u]=ed[u]=++it; co[u]=1; w[++top]=u;
    forv(v,ad[u]) if(v!=tr[u]){
        if(co[v]==0){
            tr[v]=u;
            dfs1(v);
            ed[u]=min(ed[u],ed[v]);
        } else if(co[v]==1){
            ed[u]=min(ed[u],st[v]);
        }
    }
    forv(v,adj[u]) if(v!=tr[u]){
        if(co[v]==0){
            tr[v]=u;
            dfs1(v);
            ed[u]=min(ed[u],ed[v]);
        } else if(co[v]==1){
            ed[u]=min(ed[u],st[v]);
        }
    }
    if(st[u]==ed[u]){
        scc++; int v;
        do{
            v=w[top--];
            co[v]=2;
        } while(u!=v);
    }
}

main(){
    #define task "network"
    //freopen(task".inp","r",stdin);
    //freopen(task".out","w",stdout);

    n=in;
    forinc(i,2,n){
        int u=in,v=in;
        ad[u].pb(v);
        ad[v].pb(u);
    }
    forinc(i,1,n) if(ad[i].size()==1) val.push_back(i);

    for(;;){
        shuffle(all(val),rng);
        for(int l=0;l+1<val.size();l+=2)
            add(val[l],val[l+1]);
        if(val.size()&1)
            add(val[0],val.back());
        dfs1(1);
        if(scc==1)
            break;
        ans.clear(); it=top=scc=0;
        forinc(i,1,n){
            co[i]=tr[i]=0;
            adj[i].clear();
        }
    }
    //cout<<1;
    //gg
    cout<<ans.size()<<"\n";
    forv(i,ans) cout<<i.fi<<" "<<i.se<<"\n";


}

Compilation message (stderr)

net.cpp:69:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main(){
      ^
net.cpp: In function 'int main()':
net.cpp:84:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int l=0;l+1<val.size();l+=2)
                     ~~~^~~~~~~~~~~

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 37 / 37