KMP模板

 kmp算法的最难理解的是next数组的生成，next数组存储的是匹配子串数组前缀与后缀相同长度。该next数组长度为字符串+1，next[0] = -1。

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

class KMP
{
private:
    char *str,*tar;
    int slen,tlen;
    int *next;
private:
    void getNext()
    {
        int i=0,k=-1;
        next[0] = -1;    //后一位保存着前一位的值
        while(i < tlen)
            if(k==-1 || tar[i]==tar[k])
                next[++i] = ++k;
            else k = next[k];
    }
public:
    KMP(char *s,char *t)
    {
        slen = strlen(s);
        tlen = strlen(t);
        str = new char[slen+1];  //末尾多一个字节
        tar = new char[tlen+1];
        next = new int[(tlen+1)*sizeof(int)];
        strcpy(str,s);
        strcpy(tar,t);
        getNext();
    }
    ~KMP()
    {
        if(str){delete str;str = NULL;}
        if(tar){delete tar;tar = NULL;}
        if(next){delete next;next = NULL;}
    }
    int getIndex()
    {
        int i=0,j=0;
        while(i < slen && j < tlen)
            if(j == -1 || str[i] == tar[j])
                ++i,++j;
            else j = next[j];
        if(j==tlen) return i - j;
        else return -1;
    }
    int getCount()
    {
        int i=0,j=0,cnt = 0;
        for(;i<slen;++i)
        {
            if(j > 0 && str[i] != tar[j])
                j = next[j];
            if(str[i] == tar[j]) ++j;
            if(j == tlen)
            {
                j = next[j];
                ++cnt;
            }
        }
        return cnt;
    }
};

int main()
{
    char s[100],t[100];
    while(~scanf("%s%s",s,t))
    {
        KMP kmp(s,t);
        printf("%d %d
",kmp.getIndex(),kmp.getCount());
    }
    return 0;
}

例题：

hdu2203

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
#define N (2*100000+10)
int Next[N];

void makeNext(char *Pat)
{
    int len = strlen(Pat);
    int k = 0;
    Next[0] = 0;
    for(int i=1;i<len;++i)
    {
        if(k > 0 && Pat[i] != Pat[k])
            k = Next[k-1];
        if(Pat[i] == Pat[k]) ++k;
        Next[i] = k;
    }
}
int Kmp(char *str,char *Pat)
{
    int len = strlen(str),Patlen = strlen(Pat);
    if(len < Patlen) return -1;
    string temp = str;
    temp += str;
    strcpy(str,temp.c_str());
    len = strlen(str);

    for(int i=0,j=0;i+Patlen < len;)
    {
        for(;j<Patlen;++j)
            if(str[i+j] != Pat[j]) break;
        if(j >= Patlen) return i;
        i = i + Next[j] + 1;
        j = Next[j];
    }
    return -1;
}

int main()
{
    char str1[N],str2[N];
    while(~scanf("%s%s",str1,str2))
    {
        printf("%s
",Kmp(str1,str2)!=-1?"yes":"no");
    }
    return 0;
}

hdu2594

给两个字符串，第一个前缀与第二个后缀相同，求最大len与输出相同部分字符。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string.h>
using namespace std;
#define N (100000+10)
int Next[N];

void getNext(char *str)
{
    int len = strlen(str);
    memset(Next,0,sizeof(Next));
    int i=0,k=-1;
    Next[0] = -1;
    while(i < len)
        if(k==-1 || str[i] == str[k])
            Next[++i] = ++k;
        else
            k = Next[k];
}


int main()
{
    char str[N],tar[N/2];
    while(~scanf("%s%s",str,tar))
    {
        int slen = strlen(str),tlen = strlen(tar);
        strcat(str,tar);
        getNext(str);
        int k = Next[strlen(str)];
        while(k > slen || k > tlen)
            k = Next[k];
        if(k) printf("%s ",tar+(tlen-k));
        printf("%d
",k);
    }
    return 0;
}

hdu3336

KMP+dp

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define MOD (10007)

int *Next;
int len;
void getIndex(char* str)
{
    int i=0,k=-1;
    Next[0] = -1;
    while(i < len)
        if(k==-1 || str[i] == str[k])
            Next[++i] = ++k;
        else k = Next[k];
}

int getCount(char* str)
{
    int i=0,j=0,cnt = 0;
    for(;i<len;++i)
    {
        if(j>0 && str[i] != str[j])
            j = Next[j];
        if(str[i]==str[j]) ++j,cnt = (cnt+1)%MOD;
    }
    return cnt%MOD;
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        char *str;
        scanf("%d",&len);
        str = new char[len+1];
        Next = new int[(len+1)*sizeof(int)];
        scanf("%s",str);
        getIndex(str);
        int dp[len+1];
        dp[0] = 0;
        int sum = 0;
        for(int i=1;i<=len;++i)
        {
            dp[i] = (dp[Next[i]] + 1)%MOD;
            sum = (sum + dp[i])%MOD;
        }
        printf("%d
",sum);
        delete str;
        delete Next;
        str = NULL;
        Next = 0;
    }
    return 0;
}

hdu1358（不太理解的题目）

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
class KMP
{
private:
    char *str,*tar;
    int *next;
    int slen,tlen;
private:
    void getNext()
    {
        if(tlen == 0) return;
        int i=0,k=-1;
        next[i] = k;
        while(i < tlen)
            if(k==-1 || tar[i]==tar[k])
                next[++i] = ++k;
            else k = next[k];
    }
public:
    KMP(char *s,char *t)
    {
        slen = strlen(s);
        tlen = strlen(t);
        next = new int[(tlen+1)*sizeof(int)];
        str = new char[slen+1];
        tar = new char[tlen+1];
        strcpy(str,s);
        strcpy(tar,t);
        getNext();
    }
    ~KMP()
    {
        if(next){delete next;next = NULL;}
        if(str){delete str;str = NULL;}
        if(tar){delete tar;tar = NULL;}
    }
    void showNext()
    {
        if(tlen == 0) return;
        printf("next: ");
        for(int i=0;i<=tlen;++i)
            printf("%d ",next[i]);
        printf("
");
    }
    void showAns()
    {
        for(int i=1;i<=slen;++i)
            if(i%(i-next[i])==0 && i/(i-next[i])> 1)
                printf("%d %d
",i,i/(i-next[i]));
    }

    int getIndex()
    {
        int i=0,j=0;
        while(i < slen && j < tlen)
        {
            if(j==-1 || str[i] == tar[j])
                ++i,++j;
            else j = next[j];
        }
        if(j == tlen) return i-j;
        else return -1;
    }
    int getCount()
    {
        int i=0,j=0,ans=0;
        for(;i<slen;++i)
        {
            while(j > 0 && str[i] != tar[j])
                j = next[j];
            if(str[i] == tar[j]) ++j;
            if(j == tlen)
            {
                ++ans;
                j = next[j];
            }
        }
        return ans;
    }

};
int main()
{
    char *str;
    int n;
    int t = 0;
    while(~scanf("%d",&n),n)
    {
        str = new char[n+1];
        scanf("%s",str);
        KMP kmp(str,str);
        printf("Test case #%d
",++t);
        kmp.showAns();
        if(str){delete str;str = NULL;}
        printf("
");
    }
    return 0;
}
/*
aaaa aaa
*/