KMP经典习题

KMP 算法经典题目：

pku2406 Power Strings

http://162.105.81.212/JudgeOnline/problem?id=2406

pku1961 Period

http://162.105.81.212/JudgeOnline/problem?id=1961

 这个题目是1961的升级版，考察队next数组的应用，附上代码：

#include <iostream>#include <stdio.h>#include <string.h>using namespace std;const int ma=1e6+5;char s[ma];int nex[ma];void Pre_next(int len){    int i=0,j=-1;    nex[0]=-1;    while(i<len)    {        while(j!=-1&&s[i]!=s[j]) j=nex[j];        nex[++i]=++j;    }}int main(){    int cas=1,len;    while(scanf("%d",&len)&&len)    {        scanf("%s",s);        printf("Test case #%d\n",cas++);        Pre_next(len);        int res;        for(int i=2; i<=len; ++i)        {            res=1;            if(i%(i-nex[i])==0) res=i/(i-nex[i]);            if(res>1)                printf("%d %d\n",i,res);        }        printf("\n");    }    return 0;}

pku2752 Seek the Name, Seek the Fame

http://162.105.81.212/JudgeOnline/problem?id=2752

 

pku3461 Oulipo

http://162.105.81.212/JudgeOnline/problem?id=3461

 

pku2185 Milking Grid

http://162.105.81.212/JudgeOnline/problem?id=2185

 

zjut1349 掷硬币

http://acm.zjut.edu.cn/ShowProblem.aspx?ShowID=1349

 

几道非常经典的KMP题目，很巧的利用了kmp中pre数组（前缀数组）的特性。

留题号备忘，附get_next和匹配模板。

void Get_next(int len) //目标串的长度{    int i=0,j=-1;    nex[0]=-1;    while(i<len)    {        while(j!=-1&&s[i]!=s[j]) j=nex[j];        nex[++i]=++j;    }}

int KMP_Count(int m,int n) //m:模式串长度,n:待匹配串长度{    int i,j,ans=0;    i=j=0;    Get_nex(m); //计算next[]数组    while(i<n)    {        while(j!=-1&&y[i]!=x[j]) j=nex[j];        ++i;++j;        if(j>=m)        {            ans++;            j=nex[j];        }    }    return ans;}