吉哥系列故事――完美队形II HDU - 4513(马拉车变一下形)

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define rep(i, a, n) for(int i=a; i<n; i++)
#define lap(i, a, n) for(int i=n; i>=a; i--)
#define lep(i, a, n) for(int i=n; i>a; i--)
#define rd(a) scanf("%d", &a)
#define rlld(a) scanf("%lld", &a)
#define rc(a) scanf("%c", &a)
#define rs(a) scanf("%s", a)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = 100010, INF = 0x7fffffff;
int s[maxn], s_new[maxn<<1];
int p[maxn<<1];
int n;
int init()
{
    int len = n;
    s_new[0] = -1;
    s_new[1] = -2;

    int j = 2;
    for(int i=0; i<len; i++)
        s_new[j++] = s[i], s_new[j++] = -2;
  //  s_new[j++] = -10;
    return j;
}

int manacher()
{
    int len = init();
    int max_len = -1;
    int id, mx = 0;

    for(int i=1; i<len; i++)
    {
        if(i < mx)
            p[i] = min(p[2 * id - i], mx - i);  //因为这一步最初是不执行的  所以是依附于下边的扩散步骤
        else
            p[i] = 1;
        while(s_new[i-p[i]] == s_new[i+p[i]])
        {
            if(s_new[i+p[i]] != -2 && s_new[i+p[i] - 2] < s_new[i+p[i]])  //不符合就跳出
                break;
            p[i]++;
        }
        if(mx < i + p[i])
        {
            id = i;
            mx = i + p[i];
        }
        max_len = max(max_len, p[i] - 1);
    }
    return max_len;
}

int T;
int main()
{
    rd(T);
    while(T--)
    {
        rd(n);
        rep(i, 0, n)
            rd(s[i]);
        printf("%d\n", manacher());

    }

    return 0;
}