【字符串哈希】【BKDRhash】【Rabin-Karp算法】模板

#include<cstdio>
#include<iostream>
#include<cstring>
#include<string>
#include<set>
using namespace std;
#define MAXN 100001
typedef unsigned long long ull;
const ull seed=31;
ull seeds[MAXN];
char s[MAXN],s2[MAXN];
int poss[MAXN];
//暴力字符串比较
bool Strcmp(const char a[],const int &L1,const int &R1,
const char b[],const int &L2,const int &R2)
{
	for(int i=L1,j=L2;i<R1;++i,++j)
	  if(a[i]!=b[j])
	    return 0;
	return 1;
}
//自然上溢,L首指针,R尾指针,左闭右开
ull BKDRhash(const char str[],const int &L,const int &R)
{
	ull res=0;
	for(int i=L;i<R;++i)
	  res=res*seed+str[i];
	return res;
}
//预处理,便于hash(s[i...i+m-1]和hash(s[i+1...i+m]之间的转移) 
void init_seeds()
{
	seeds[0]=1;
	for(int i=1;i<MAXN;++i)
	  seeds[i]=seeds[i-1]*seed;
}
//文本串查找,s文本串,sub子串
int RabinKarp(const char s[],const char sub[])
{
	int n=strlen(s),m=strlen(sub);
	ull hsub=BKDRhash(sub,0,m),hs=BKDRhash(s,0,m);
	for(int i=0;i<=n-m;++i)
	  {
	  	if(hs==hsub && Strcmp(s,i,i+m,sub,0,m))
	      return i;
	    hs=(hs-s[i]*seeds[m-1])*seed+s[i+m];//O(1)转移 
	  }
	return -1;
}
int main()
{
	init_seeds();
	while(1)
	  {
	  	scanf("%s%s",s,s2);
	  	printf("%d
",RabinKarp(s,s2));
	  }
	return 0;
}