分析：很无奈，我想用python。实在是简单呀。

python:

s1 = raw_input()
s2 = raw_input()
for e in s2:
    if e in s1:
        s1 = s1.replace(e, '')
print s1

c++:

#include <iostream>
#include <string>
#include <map>
#include <vector>
#include <algorithm>
using namespace std;
  
int main() {  
    string s, st;
	getline(cin, s);
	getline(cin, st);
	for(int i = 0; i < s.length(); i++){
		for(int j = 0; j < st.length(); j++){
			if(s[i] == st[j]){
				s[i] = '-';
				break;
			}
		}
	}
	for(int i = 0; i < s.length(); i++){
		if(s[i] != '-') printf("%c", s[i]);
	}
	cout << endl;
    return 0;  
}