poj 3461 字符串单串匹配--KMP或者字符串HASH

Posted 2020-09-26 yangykaifa

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

先来一发KMP算法：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <cmath>
#include <map>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdin)

const int MAXN = 1000000+100;
char T[MAXN],P[MAXN],tmp[MAXN];//T--文本，P--模板串
int fail[MAXN];
void getfail()
{
    int m=strlen(P);
    fail[0]=fail[1]=0;
    for(int i=1;i<m;i++)
    {
        int j=fail[i];
        while(j && P[i]!=P[j])j=fail[j];
        fail[i+1]=P[i]==P[j]?j+1:0;
    }
}

int Find()
{
    int ans=0;
    int n=strlen(T),m=strlen(P);
    if(n<m)
    {
        strcpy(tmp,T);
        strcpy(T,P);
        strcpy(P,tmp);
    }
    getfail();
    int j=0;
    for(int i=0;i<n;i++)
    {
        while(j && P[j]!=T[i])j=fail[j];
        if(P[j] == T[i])j++;
        if(j==m)//printf("%d\n",i-m+1);//find it
            ans++;
    }
    return ans;
}

int main()
{
    //IN("poj3461.txt");
    int n;
    while(~scanf("%d",&n))
    {
        while(n--)
        {
            scanf("%s%s",P,T);
            printf("%d\n",Find());
        }

    }
    return 0;
}

再来一发字符串HASH

我的字符串HASH模板在http://blog.csdn.net/u011026968/article/details/38460357

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <cmath>
#include <map>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdin)
#define ull unsigned long long
const ull B = 1e8+7;    /*according to the book*/
const int MAXN = 1000000+100;
char a[MAXN],b[MAXN],tmp[MAXN];

int hashfind()
{
    int ans=0;
    int al=strlen(a),bl=strlen(b);
    if(al>bl)
    {
        strcpy(tmp,a);
        strcpy(a,b);
        strcpy(b,tmp);
    }
    ull t=1,ah=0,bh=0;
    for(int i=0;i<al;i++)
    {
        t*=B;
        ah=ah*B+a[i];
        bh=bh*B+b[i];
    }
    for(int i=0;i+al<=bl;i++)
    {
        if(ah==bh)ans++;
        if(i+al<bl)bh=bh*B+b[i+al]-b[i]*t;
    }
    return ans;
}


int main()
{
    //IN("poj3461.txt");
    int n;
    while(~scanf("%d",&n))
    {
        while(n--)
        {
            scanf("%s%s",a,b);
            printf("%d\n",hashfind());
        }

    }
    return 0;
}