1050-String-Subtraction.md

title	<Python><PAT> 1050 String Subtraction
date	2019-08-27 06:22:24 -0700
tags	PAT 题解 哈希集合 字符串
cover	http://pwb80dtf4.bkt.clouddn.com/PAT-cover.webp
categories	PAT
top_img	http://pwb80dtf4.bkt.clouddn.com/PAT-top.webp
description	字符串大水题

题目

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.

题解

思路

• 对第一行字符串的每个字符，如果它不在第二行当中，那么就输出它。
• 很显然用哈希集合。

数据结构

• a是第一行，字符串
• b是一个哈希集和，存放第二行每一个字符。

算法

• 先输入第一行
• 再输入第二行，建哈希集和
• 对每一个第一行的字符，判断其在不在第二行，不在就输出，注意后面不加空格。

代码

• 因为使用Python能够AC，因此只放了Python的代码。

a = input()
b = set([i for i in input()])
for i in a:
    if i not in b:
        print(i, end='')