HDU 4513 吉哥系列故事——完美队形II（Manacher)

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<cmath>
#include<map>
#include<stack>
#include<bitset>
using namespace std;
#define REPF( i , a , b ) for ( int i = a ; i <= b ; ++ i )
#define REP( i , n ) for ( int i = 0 ; i < n ; ++ i )
#define CLEAR( a , x ) memset ( a , x , sizeof a )
typedef long long LL;
typedef pair<int,int>pil;
const int INF = 0x3f3f3f3f;
const int maxn=1e6+100;
int str[maxn];
int temp[maxn<<1];
int Len[maxn<<1];
int t,n;
int init()
{
    int i,len=n;
    temp[0]=0;
    for(int i=1;i<=2*len;i+=2)
    {
        temp[i]=-1;
        temp[i+1]=str[i/2];
    }
    temp[2*len+1]=-1;
    temp[2*len+2]=1;
    return 2*n+1;
}
int Manacher()
{
    int len=init();
    int mx=0,ans=0,po=0;//mx:靠右位置,po:i值
    for(int i=1;i<=len;i++)
    {
        if(mx>i)  Len[i]=min(mx-i,Len[2*po-i]);
        else Len[i]=1;
        while(temp[i-Len[i]]==temp[i+Len[i]])
        {
            if(Len[i]==1)  Len[i]++;
            else if(temp[i-Len[i]]==-1&&temp[i-Len[i]+1]<=temp[i-Len[i]+3])
               Len[i]++;
            else if(temp[i-Len[i]]!=-1&&temp[i-Len[i]]<=temp[i-Len[i]+2])
               Len[i]++;
            else break;
        }
        if(Len[i]+i>mx)
        {
            mx=Len[i]+i;
            po=i;
        }
        ans=max(ans,Len[i]);
    }
    return ans-1;//Len[i]-1；
}
int main()
{
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        REP(i,n)  scanf("%d",&str[i]);
        printf("%d\n",Manacher());
    }
    return 0;
}