POJ3461一道kmp题，字符串Hash也可

题目链接：http://icpc.njust.edu.cn/Problem/Pku/3461/

代码如下：

#include<cstdio>
#include<string.h>
using namespace std;
typedef unsigned int ui;
typedef long long ll;
typedef unsigned long long ull;
#define pf printf
#define mem(a,b) memset(a,b,sizeof(a))
#define prime1 1e9+7
#define prime2 1e9+9
#define pi 3.14159265
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define scand(x) scanf("%llf",&x) 
#define f(i,a,b) for(int i=a;i<=b;i++)
#define scan(a) scanf("%d",&a)
#define dbg(args) cout<<#args<<":"<<args<<endl;
#define inf 0x3f3f3f3f
#define maxn 1000010
int n,m,t;
ull Hash[maxn],h[maxn];
char a[maxn],b[maxn];
const int p=131;
void init()
{
    h[0]=1;
    f(i,1,maxn-1)
    {
        h[i]=h[i-1]*p;
    }
 } 
 
int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    //std::ios::sync_with_stdio(false);
    scan(t); 
    init();
    while(t--)
    {
        scanf("%s%s",&a,&b);
        int lena=strlen(a);
        int lenb=strlen(b);
        int ans=0;
        int hasha=a[0]-'a',hashb;
        f(i,1,lena-1)
        {
            hasha=hasha*p+a[i]-'a';
        }
        Hash[0]=b[0]-'a';
        f(i,1,lenb-1)
        {
            Hash[i]=Hash[i-1]*p+b[i]-'a';
        }
        f(i,0,lenb-lena)
        {
            int l=i;
            int r=l+lena-1;
            hashb=Hash[r]-Hash[l-1]*h[lena];
            if(hasha==hashb)ans++;
        //    dbg(ans);
        }
        pf("%d
",ans);
    }
 }