ural1297 求最长回文子串 | 后缀数组

#include<cstdio>
#include<algorithm>
#include<cstring>
#define N 20005
using namespace std;
int buf1[N],buf2[N],sa[N],rnk[N],buc[N],n,height[N],ans,Log[N],pos,Min[N][];
char s[N];
void suffix_sort()
{
    int *x=buf1,*y=buf2,m=;
    for (int i=;i<m;i++) buc[i]=;
    for (int i=;i<=n;i++) buc[x[i]=s[i]]++;
    for (int i=;i<=m;i++) buc[i]+=buc[i-];
    for (int i=n;i;i--) sa[buc[x[i]]--]=i;
    for (int k=;k<=n;k<<=)
    {
        int  p=;
        for (int i=n-k+;i<=n;i++)
            y[++p]=i;
        for (int i=;i<=n;i++)
            if (sa[i]>k) y[++p]=sa[i]-k;
        for (int i=;i<=m;i++) buc[i]=;
        for (int i=;i<=n;i++) buc[x[y[i]]]++;
        for (int i=;i<=m;i++) buc[i]+=buc[i-];
        for (int i=n;i;i--) sa[buc[x[y[i]]]--]=y[i];
        swap(x,y),x[sa[]]=p=;
        for (int i=;i<=n;i++)
            if (y[sa[i-]]==y[sa[i]] && y[sa[i-]+k]== y[sa[i]+k])
                x[sa[i]]=p;
             else x[sa[i]]=++p;
        if ((m=p)>=n) break;
    }
    for (int i=;i<=n;i++)
    rnk[sa[i]]=i;
    for (int i=,j,k=;i<=n;i++)
    {
        if (rnk[i]==) continue;
        if (k) k--;
        j=sa[rnk[i]-];
        while (s[i+k]==s[j+k] && i+k<=n && j+k<=n) k++;
        height[rnk[i]]=k;
    }
}
void InitRmq()
{
    for (int i=;i<=n;i++) Min[i][]=height[i];
    for (int j=;j<=;j++)
    for (int i=;i+(<<j)-<=n;i++)
        Min[i][j]=min(Min[i][j-],Min[i+(<<j-)][j-]);
}
int Query(int x,int y)
{
    int i=rnk[x],j=rnk[y];
    if (i>j) swap(i,j);
    int len=Log[j-i];
    return min(Min[i+][len],Min[j-(<<len)+][len]);
}
int main()
{
    scanf("%s",s+);
    n=strlen(s+);
    if (n==)
    {
    puts(s+);
    return ;
    }
    s[n+]='#';
    for (int i=;i<=n;i++)
    s[*n+-i]=s[i];
    n=n*+;
    suffix_sort();
    for (int i=;i<=n;i++)
    Log[i]=Log[i>>]+;
    InitRmq();
    for (int i=;i<=(n-)/;i++)
    {
    int tmp=Query(i,n-i+);
    if (tmp*>ans) ans=tmp*,pos=i-tmp;
    tmp=Query(i,n-i+);
    if (tmp*->ans) ans=tmp*-,pos=i-tmp+;
    }
    for (int i=;i<=ans;i++)
    putchar(s[i+pos-]);
    return ;
}