HDU 4513 单增回文 manacher

#include<cstring>
#include<cstdio>
#include<map>
#include<string>
#include<algorithm>
#include<iostream>
using namespace std;
int a[100010],s1[201111],p[201111],n;
int manacher()
{
int ans = 0;
for(int i=1;i<=n;i++)
{
s1[i*2-1] = -1;
s1[i*2] = a[i];
}
s1[0] = -2;
s1[n*2+1] = -1;
s1[n*2+2] = -3;
int Max = 0,MaxId = 0;
for(int i=1;i<=2*n+1;i++)
{
p[i] = i>=Max?1:min(p[2*MaxId-i],Max-i);
while(s1[i+p[i]]==s1[i-p[i]]&&(s1[i-p[i]]<0||s1[i-p[i]]<=s1[i-p[i]+2]))p[i]++;
if(i+p[i]>Max)
{
MaxId = i;
Max = i+p[i];
}
ans = max(p[i]-1,ans);
}
return ans;
}
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
for(int i=1;i<=n;i++)scanf("%d",&a[i]);
printf("%d\n",manacher());
}
return 0;
}