7-51代码：（map)

#include<iostream>
#include<map>
using namespace std;
map<int,int>mp;
int cnt,cnttp;
void scan(){
    while(1){
		int x; scanf("%d",&x);
		if(x==-1) break;
		mp[x]++;cnt++;
	}	
}
int main(){
	scan();scan();
	if(!mp.size()) printf("NULL");
	for(auto it=mp.begin();it!=mp.end();it++){
		while(it->second--){
	    	cnttp++;
		    if(cnttp==cnt) printf("%d",it->first);
	    	else printf("%d ",it->first);
	    }
	}
	return 0;
}

 7-52代码：(map+vector)

#include<iostream>
#include<map>
#include<vector>
using namespace std;
map<int,int>mp;
vector<int>vc;
int main(){
	while(1){
		int x; scanf("%d",&x);
		if(x==-1) break;
		mp[x]++;
	}
	while(1){
		int x; scanf("%d",&x);
		if(x==-1) break;
		if(mp[x]){
		    mp[x]--;
			vc.push_back(x);
		}
	}
	if(!vc.size()) printf("NULL");
	else{
		for(int i=0;i<vc.size()-1;i++)
		    printf("%d ",vc[i]);
	    printf("%d",vc[vc.size()-1]);
	}
	return 0;
}