题解 100% AC

#include <bits/stdc++.h>
using namespace std;
int a[5010],b[1000010];
int main(){
	int n;cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        if(b[a[i]]==0){
        	cout<<a[i]<<" ";
            b[a[i]]++;
        }
    }
}