PAT1050. String Subtraction

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 10⁴. 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.
思路：提示时间短的话一定要记住哈希，哈希就是用空间换时间。

 1 #include <iostream>
 2 #include <cstring>
 3 using namespace std;
 4
 5 bool Harsh[128]={
 6     false
 7 };
 8 #define MAX 10010
 9 char str1[MAX];
10 char str2[MAX];
11 int main(int argc, char *argv[])
12 {
13     gets(str1);
14     int i=0;
15     for(char ch=getchar();ch!=‘\n‘;ch=getchar())
16     {
17         Harsh[ch]=true;
18         str2[i++]=ch;
19     }
20     for(int i=0;str1[i]!=‘\0‘;i++)
21     {
22         if(!Harsh[str1[i]])
23            putchar(str1[i]);
24     }
25     putchar(‘\n‘);
26     return 0;
27 }