Submission #559601

#	Time	Username	Problem	Language	Result	Execution time	Memory
559601		zaneyu	Network (BOI15_net)	C++14	100 / 100	453 ms	43784 KiB

net

/*input
5
1 2
1 3
*/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
//order_of_key #of elements less than x
// find_by_order kth element
typedef unsigned long long int ll;

#define ld long double
#define pii pair<int,int>
typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;
#define f first
#define s second
#define pb push_back
#define REP(i,n) for(int i=0;i<n;i++)
#define REP1(i,n) for(int i=1;i<=n;i++)
#define FILL(n,x) memset(n,x,sizeof(n))
#define ALL(_a) _a.begin(),_a.end()
#define sz(x) (int)x.size()
const ll maxn=5e5+5;
const ll maxlg=__lg(maxn)+2;
const ll INF64=4e18;
const int MOD=1e9+7;
const int INF=0x3f3f3f3f;
const ld PI=acos(-1);
const ld eps=1e-9;
#define lowb(x) x&(-x)
#define MNTO(x,y) x=min(x,(__typeof__(x))y)
#define MXTO(x,y) x=max(x,(__typeof__(x))y)
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
template<typename T1,typename T2>
ostream& operator<<(ostream& out,pair<T1,T2> P){
    out<<P.f<<' '<<P.s;
    return out;
}
template<typename T>
ostream& operator<<(ostream& out,vector<T> V){
    REP(i,sz(V)) out<<V[i]<<((i!=sz(V)-1)?" ":"");
    return out;
}
ll mult(ll a,ll b){
    if(a<0) a+=MOD;
    return (a*b)%MOD;
}
ll mypow(ll a,ll b){
    if(b<=0) return 1;
    ll res=1LL;
    while(b){
        if(b&1) res=mult(res,a);
        a=mult(a,a);
        b>>=1;
    }
    return res;
}
int in[maxn];
int cur=0;
vector<int> v[maxn];
void dfs(int u,int p){
    in[u]=cur++;
    for(int x:v[u]){
        if(x==p) continue;
        dfs(x,u);
    }
}
bool cmp(int a,int b){
    return in[a]<in[b];
}
int32_t main(){
    ios::sync_with_stdio(false),cin.tie(0);
    int n;
    cin>>n;
    REP(i,n-1){
        int a,b;
        cin>>a>>b;
        --a,--b;
        v[a].pb(b),v[b].pb(a);
    }
    vector<int> vv;
    REP(i,n) if(sz(v[i])==1){
        vv.pb(i);
    }
    dfs(0,-1);
    sort(ALL(vv),cmp);
    if(sz(vv)%2) vv.pb(vv[0]);
    cout<<sz(vv)/2<<'\n';
    REP(i,sz(vv)/2){
        cout<<vv[i]+1<<' '<<vv[i+sz(vv)/2]+1<<'\n';
    }
}   

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