HDU 4513 吉哥系列故事——完美队形II

 1 //#define LOCAL
 2 #include <iostream>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <algorithm>
 6 using namespace std;
 7 
 8 const int maxn = 100000 + 10;
 9 int n;
10 int a1[maxn], a2[maxn * 2], p[maxn * 2];
11 
12 void Init(void)
13 {
14     int id, mx = 0, j = 2;
15     a2[0] = -1, a2[1] = 0;
16     for(int i = 0; i < n; ++i)
17     {
18         a2[j++] = a1[i];
19         a2[j++] = 0;
20     }
21 }
22 
23 void Manacher(int a[])
24 {
25     int mx = 0, id;
26     p[0] = 0;
27     for(int i = 0; i < (n+1)*2; ++i)
28     {
29         if(mx > i)
30             p[i] = min(p[id*2-i], mx-i);
31         else
32             p[i] = 1;
33         while(a[i+p[i]] == a[i-p[i]])
34         {
35             if(a[i-p[i]])
36             {
37                 if(a[i-p[i]] <= a[i-p[i]+2])
38                     ++p[i];
39                 else
40                     break;
41             }
42             else
43                 ++p[i];
44         }
45         if(mx < i + p[i])
46         {
47             mx = i + p[i];
48             id = i;
49         }
50     }
51 }
52 
53 void getans(void)
54 {
55     int ans = 1;
56     for(int i = 1; i < (n+1)*2; ++i)
57         ans = max(ans, p[i] - 1);
58     printf("%d\n", ans);
59 }
60 
61 int main(void)
62 {
63     #ifdef LOCAL
64         freopen("4513in.txt", "r", stdin);
65     #endif
66 
67     int T;
68     scanf("%d", &T);
69     while(T--)
70     {
71         scanf("%d", &n);
72         for(int i = 0; i < n; ++i)
73             scanf("%d", &a1[i]);
74         Init();
75         Manacher(a2);
76         getans();
77     }
78     return 0;
79 }