SCU-4438 Censor（字符串HASH）

最新推荐文章于 2019-08-13 09:39:21 发布

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本文介绍了一个使用哈希算法处理敏感词删除的问题。通过计算敏感词的哈希值，并利用栈来辅助处理文本中的匹配和删除过程，实现了高效的文本过滤。

哈希模板：挑战程序设计P374

Censor

frog is now a editor to censor so-called sensitive words (敏感词).

She has a long text p. Her job is relatively simple -- just to find the first occurence of sensitive word w and remove it.

frog repeats over and over again. Help her do the tedious work.

Input

The input consists of multiple tests. For each test:

The first line contains 1 string w. The second line contains 1 string p.

(1≤length of w,p≤5⋅106, w,p consists of only lowercase letter)

Output

For each test, write 1 string which denotes the censored text.

Sample Input

    abc
    aaabcbc
    b
    bbb
    abc
    ab

Sample Output

    a
    
    ab

题意：每次删去字符串b中的a串，输出最终剩余的字符

思路：将a串哈希为一个整数，将b字符依次放入栈中，当长度大于等于a串的长度时，比较哈希值，相同则删除，继续操作

CODE：

#include<stdio.h>
#include<vector>
#include<iostream>
#include<string.h>
#include<queue>
#include<algorithm>
using namespace std;
typedef unsigned long long ull;
const ull B =1e8+7;//哈希的基数  
const int N=5*1e6+10;
ull bh[N];
char a[N],b[N],str[N];
int main()
{
    while(~scanf("%s%s",a,b))
    {
        int a1=strlen(a),b1=strlen(b);
        if(a1>b1)
        {
            printf("%s\n",b);
            continue;
        }
        ull t=1;
       for(int i=0; i<a1; i++)
        {
             t*=B;
        }
        ull ah=0;
        bh[0]=0;
        for(int i=0; i<a1; i++) ah=ah*B+a[i];
      //  printf("%llu \n",ah);
        int top=0;
        for(int i=0;i<b1;i++)
        {
            str[top++]=b[i];
            bh[top]=bh[top-1]*B+b[i];
            
            if(top>=a1&&bh[top]-bh[top-a1]*t==ah)
            {
                //printf("%d\n",top);
                top-=a1;
            }

        }
       for(int i=0;i<top;i++)
       {
           printf("%c",str[i]);
       }
       printf("\n");
    }
}