poj_1974，最长回文字串manacher

时间复杂度为O(n)，参考：http://bbs.dlut.edu.cn/bbstcon.php?board=Competition&gid=23474

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 2001000
using namespace std;
char s[maxn],st[maxn];
int p[maxn];
int cases=1;
int n;
void rebuild()
{
    st[0]='$';
    st[1]='#';
    int len=strlen(s);
    for(int i=0;i<len;i++)
        {st[2*i+2]=s[i];st[2*i+3]='#';}
    st[2*len+2]=0;
}
void solve()
{
    int len=2*strlen(s)+2;
    int id,mx=0,ans=1;
    for(int i=0;i<len;i++)
    {
        if(mx>i)
            p[i]=min(p[2*id-i],mx-i);
        else
            p[i]=1;
        for(;st[p[i]+i]==st[i-p[i]];p[i]++)
            ;
        if(p[i]+i>mx)
        {
            mx=p[i]+i;
            id=i;
        }
        ans=max(ans,p[i]);
    }
    cout<<"Case "<<cases++<<": "<<ans-1<<endl;
}
int main()
{
    while(gets(s))
    {
        if(s[0]=='E'&&s[1]=='N'&&s[2]=='D') break;
        rebuild();
        solve();
    }
    return 0;
}