Manacher

Manacher

#define maxn 1000050
char s[maxn];
char ss[2*maxn];
int p[2*maxn];
int manacher(char s[],int len)
{
    int i,j,len1;
    for(i=0;i<2*len+2;i++)ss[i]='#';
    for(i=0;i<len;i++)ss[i*2+2]=s[i];
    len1=len*2+1;ss[0]='$';
    int mx=0,id=0;
    int ans=0;
    for(int i=0;i<len1;i++){
        p[i]=mx>i?min(p[2*id-i],mx-i ):1;
        while(ss[i+p[i] ]==ss[i-p[i] ] )p[i]++;
        if(ans<p[i])ans=p[i];
        if(i+p[i]>mx){
            mx=i+p[i];
            id=i;
        }
    }
    return ans-1;
}