[PAT-A] 1050 String Subtraction

Java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.HashSet;
import java.util.Set;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String s1 = br.readLine();
        String s2 = br.readLine();

        Set<Character> st = new HashSet<>();
        for (int i = 0; i < s2.length(); i++) {
            st.add(s2.charAt(i));
        }

        StringBuilder res = new StringBuilder();
        for (int i = 0; i < s1.length(); i++) {
            if (!st.contains(s1.charAt(i))) {
                res.append(s1.charAt(i));
            }
        }

        System.out.println(res);
    }
}

C++

#include <iostream>
#include <cstring>
#include <algorithm>
#include <unordered_set>

using namespace std;

const int MAXN = 10010;

string s1, s2;
unordered_set<char> st;

int main() {
    getline(cin, s1);
    getline(cin, s2);

    for (int i = 0; i < s2.size(); i++) st.insert(s2[i]);

    string res;
    for (int i = 0; i < s1.size(); i++) {
        if (!st.count(s1[i])) res += s1[i];
    }

    cout << res << endl;
    return 0;
}