题解

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define ll long long 
const ll N=2e5+5;
ll a[N];
map<ll,vector<ll> >mp;
int main(){
	freopen("merge.in","r",stdin);
	freopen("merge.out","w",stdout);
	ll n;
	cin>>n;
	for(ll i=1;i<=n;i++){
		cin>>a[i];
		mp[a[i]].pb(i);
	}
	for(auto p:mp){
		vector<ll> v=p.second;
		sort(v.begin(),v.end());
		ll m=v.size();
		for(ll i=1;i<m;i+=2){
			a[v[i-1]]=0;
			a[v[i]]*=2;
			mp[a[v[i]]].pb(v[i]);
		}
	}
	ll num=0;
	for(ll i=1;i<=n;i++){
		if(a[i]!=0){
			num++;
		}
	}
	cout<<num<<'\n';
	for(ll i=1;i<=n;i++){
		if(a[i]!=0){
			cout<<a[i]<<' ';
		}
	}
	fclose(stdin);
    fclose(stdout);
}