Manacher算法

来源：互联网发布：减少数据库访问次数编辑：程序博客网时间：2024/05/04 21:20

http://blog.csdn.net/ggggiqnypgjg/article/details/6645824/

原文说的很清楚，Manacher算法就是O(n)来求一个字符串S的最长回文串的。

hdu3068

#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <algorithm> //max min函数包含在这个里面。。？using namespace std;#define LEN 110010char s[LEN],s1[LEN*2];//长度一定要*2 !!int p[LEN*2];int n;void pre(){    n=strlen(s);    s1[0]='$';//防止比较的时候越界    s1[1]='#';    for (int i=0;i<n;i++)    {        s1[(i+1)*2]=s[i];        s1[(i+1)*2+1]='#';    }    n=n*2+2;    s1[n]=0;}void kp(){    int mx=0;    int id;    for (int i=1;i<=n;i++)    {        if (mx>i)            p[i]=min(p[2*id-i],mx-i); //这里的两种情况使得算法O(n）        else            p[i]=1;        while(s1[i-p[i]]==s1[i+p[i]]) p[i]++;        if (i+p[i]>mx)        {            mx=i+p[i];            id=i;        }    }}void pt(){    int ans=0;    for (int i=1;i<=n;i++)       ans=max(ans,p[i]-1);    printf("%d\n",ans);}int main(){    while (~scanf("%s",s))    {        pre();        kp();        pt();    }}

ural1297

#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <algorithm>using namespace std;#define LEN 110010char s[LEN],s1[LEN*2];//长度一定要*2 !!int p[LEN*2];int n;void pre(){    n=strlen(s);    s1[0]='$';//防止比较的时候越界    s1[1]='#';    for (int i=0;i<n;i++)    {        s1[(i+1)*2]=s[i];        s1[(i+1)*2+1]='#';    }    n=n*2+2;    s1[n]=0;}void kp(){    int mx=0;    int id;    for (int i=1;i<=n;i++)    {        if (mx>i)            p[i]=min(p[2*id-i],mx-i);        else            p[i]=1;        while(s1[i-p[i]]==s1[i+p[i]]) p[i]++;        if (i+p[i]>mx)        {            mx=i+p[i];            id=i;        }    }}void pt(){    int ans=0;    int id;    for (int i=1;i<=n;i++)        if (ans<p[i])        {            ans=p[i];            id=i;        }    for (int i=id-ans+1;i<=id+ans-1;i++)        if (s1[i]!='#') cout<<s1[i];}int main(){    while (~scanf("%s",s))    {        pre();        kp();        pt();    }}

感觉很奇怪，原文作者说他的代码有bug，然而我没加str[]清空，似乎没有bug。。？

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