不多说，粘代码

#include<bits/stdc++.h>
using namespace std;
#define file(FILENAME) freopen(FILENAME".in","r",stdin),freopen(FILENAME".out","w",stdout)
#define DBG cerr << __LINE__ << ' ' << __FUNCTION__ << endl
#define _rep(i,a,b,o) (for(int ((i)=(a));((i)<(b));((i)+=(o))))
#define ll long long
#define PI acos(1.0)
#define endl "\n"
#define swap(a,b) int utc=a;a=b;b=utc;
#define abs(a) ((a<0)?(a=-a):(a=a))
#define INF 0x3f3f3f3f
#define max(a,b) ((a>b)?(a):(b))
#define min(a,b) ((a<b)?(a):(b))
int bucket[1005];
int main(){
    int n;
    scanf("%d",&n);
    int i;
    for(i=0;i<n;i+=1){
        int num;
        scanf("%d",&num);
        bucket[num]=1;
    }
    int sum=0;
    for(i=0;i<n;i+=1){
        if(bucket[i+1]==1) sum++;
    }
    printf("%d",sum);
    printf("\n");
    for(i=0;i<n;i+=1){
        if(bucket[i+1]) printf("%d ",i+1);
    }
    return 0;
}

另外，P1059