[？？？] Codeforces Round #671 (Div. 2) D2. Sage's Birthday (hard version)

题目：http://codeforces.com/contest/1419/problem/D2

本来写的是easy version的代码，交hard version竟然能过

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,a,b) for(ll i=a;i<=b;i++)
#define endl '\n'
#define V vector
#define pb(x) push_back(x);
const ll amn=1e5+5;
ll a[amn];
int main(){
    ios::sync_with_stdio(0);
    ll T=1;
//    cin>>T;
    while(T--){
        ll n;cin>>n;
        rep(i,1,n){
            cin>>a[i];
        }
        sort(a+1,a+1+n);
        V<ll> aa,bb,ans;
        aa.clear();
        bb.clear();
        ans.clear();
        rep(i,1,n/2)aa.pb(a[i]);
        rep(i,n/2+1,n)bb.pb(a[i]);

//        cout<<n/2<<' '<<aa.size()<<' '<<bb.size()<<endl;
        for(ll i=0,j=0;i<aa.size()||j<bb.size();i++,j++){
            if(j<bb.size())ans.pb(bb[i]);
            if(i<aa.size())ans.pb(aa[i]);

        }
        ll cnt=0;
        rep(i,0,ans.size()-1){
            if(i-1>=0&&i+1<ans.size()&&ans[i-1]>ans[i]&&ans[i]<ans[i+1])cnt++;
        }
        cout<<cnt<<endl;
        rep(i,0,ans.size()-1)cout<<ans[i]<<' ';cout<<endl;
    }
}