PAT--1050 String Subtraction (20 分)

Given two strings S​1​​ and S​2​​, S=S​1​​−S​2​​ is defined to be the remaining string after taking all the characters in S​2​​ from S​1​​. Your task is simply to calculate S​1​​−S​2​​ for any given strings. However, it might not be that simple to do it fast.

Input Specification:

Each input file contains one test case. Each case consists of two lines which gives S​1​​ and S​2​​, respectively. The string lengths of both strings are no more than 10​4​​. It is guaranteed that all the characters are visible ASCII codes and white space, and a new line character signals the end of a string.

Output Specification:

For each test case, print S​1​​−S​2​​ in one line.

Sample Input:

They are students.
aeiou

Sample Output:

Thy r stdnts.

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{

    string str,sub;
    getline(cin,str);
    getline(cin,sub);

    for(int i=0; i<str.length(); i++)
    {
        int flag = 0;
        for(int j=0; j<sub.length(); j++)
        {
            if(str[i]==sub[j])
            {
                flag = 1;
                break;
            }
        }
        if(flag==0)
        {
            cout<<str[i];
        }
    }
    cout<<endl;
    //cout<<result<<endl;
    //cout<<sub<<endl;
    return 0;
}

 注：

本来在判断的时候加了个在等于空格的是时候不算，结果提交了几次错了。