2019-05-21 P1059

题目链接：https://www.luogu.org/problemnew/show/P1059

#include<map>
#include<cstdio>
using namespace std;
int n,x,cnt;
int main(void){
    map<int,int>mp;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%d",&x);
        if(mp[x]==0){
            cnt++;
            mp[x]=1;
        }
        else{
            mp[x]++;
        }
    }
    
    printf("%d\n",cnt);
    
    int i=1;
    while(cnt>0){
        if(mp[i]>0){
            cnt--;
            printf("%d",i);
            if(cnt==0) printf("\n");
            else printf(" ");
        }
        i++;
    }
    return 0;
}