PAT (Advanced Level) Practice 1050 String Subtraction（20分）【哈希】

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.

题意

读入两个字符串，输出第一个字符串，但是略过在第二个字符串中出现过的字符。

思路

使用set。

代码

#include <iostream>
#include <set>
#include <string>

using namespace std;

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

    set<char> st;

    for (auto &i : s2)
        st.insert(i);

    for (auto &i : s1)
        if (!st.count(i))
            cout << i;
}