POJ 3461 Oulipo hash求匹配

题目：

http://poj.org/problem?id=3461

题意：

给一个模式串，一个原串，问原串中有多少个模式串

思路：

kmp模板题，这里用hash算法

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef long long ll;typedef unsigned long long ull;const int N = 1000000 + 10, M = 10000 + 10, INF = 0x3f3f3f3f;const int seed = 31;//31,131,1313,13131,131313...char pat[M], ori[N];ull Seed[N], hash_ori[N];ull BKDRhash(char *str){    ull h = 0;    for(int i = 0; str[i]; i++)        h = h * seed + str[i];    return h;}int main(){    Seed[0] = 1;    for(int i = 1; i < N; i++) Seed[i] = Seed[i-1] * seed;    int t;    scanf("%d", &t);    while(t--)    {        scanf("%s%s", pat+1, ori+1);        ull hash_pat = BKDRhash(pat+1);        int len_pat = strlen(pat+1);        hash_ori[0] = 0;        int ans = 0;        for(int i = 1; ori[i]; i++)        {            hash_ori[i] = hash_ori[i-1] * seed + ori[i];//也是BKDRhash            int j = i - len_pat + 1;            if(j >= 1)            {                if(hash_ori[i] - hash_ori[j-1]*Seed[len_pat] == hash_pat) ans++;            }        }        printf("%d\n", ans);    }    return 0;}