PAT A1050:String Subtraction之哈希映射

题目描述

1050 String Subtraction (20分)
Given two strings S1 and S2, S=S1-S2 is defined to be the remaining string after taking all the characters in S2 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.

Input Specification:
Each input file contains one test case. Each case consists of two lines which gives S1 and S2, 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 S1-S2 in one line.

Sample Input:

They are students.
aeiou

Sample Output:

Thy r stdnts.

求解思路

将s2中出现的字符映射到哈希表中,然后在s1中开始遍历哈希表,如果当前s1中的字符曾在哈希表中出现过,那么则不输出。

代码实现(AC)
#includeiostream
#includecstring
#includestring
using namespace std;
const int maxn=256;
int hashTable[maxn]={0};
int main()
{
	string s1,s2;
	getline(cin,s1);
	getline(cin,s2);
	for(int i=0;is2.length();i++)
		hashTable[s2[i]]=1;
	for(int i=0;is1.length();i++)
	{
		if(!hashTable[s1[i]])	couts1[i];
	} 
	return 0;
} 
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