PAT（甲级）1050.String Subtraction（20）

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PAT 1050.String Subtraction（20）

Given two strings S1 and S​2​​ , S=S1−S​2 is defined to be the remaining string after taking all the characters in S​2 from S1. Your task is simply to calculate S1−S2 for any given strings. However, it might not be that simple to do it fast.

输入格式：
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.

输出格式：
For each test case, print S​1−S2 in one line.

输入样例：

They are students.
aeiou

输出样例：

Thy r stdnts.

题目分析：数组hash的使用，因为题目要求s1-s2,因此开辟一个hash数组用来存放s2中出现的字符，然后遍历s1的所有字符，如果在hash数组中出现过就不输出。

注意：题目给出的字符串可能包含空格，因此不能使用cin进行输入，建议使用getline()进行输入。

AC代码：

#include <iostream>
#include <string>
using namespace std;
const int maxn = 128;
bool is_appear[maxn]={false};

int main(){
    string s1,s2;
    getline(cin, s1);
    getline(cin, s2);
    for(int i=0; i<s2.length(); ++i){
        is_appear[s2[i]] = true;
    }
    for(int i=0; i<s1.length(); ++i){
        if(!is_appear[s1[i]])
            cout<<s1[i];
    }
    return 0;
}