HDU 4513 吉哥系列故事——完美队形II（Manacher）

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 using namespace std;
 6 
 7 const int MAXN = 100010;
 8 
 9 int p[MAXN << 1], s[MAXN << 1];
10 int n, cnt, T;
11 
12 void manacher() {
13     int mx = 0, id;
14     for(int i = 1; i < cnt; ++i) {
15         if(mx > i) p[i] = min(p[2 * id - i], mx - i);
16         else p[i] = 1;
17         while(s[i + p[i]] == s[i - p[i]] && s[i + p[i]] <= s[i + p[i] - 2]) ++p[i];
18         if(i + p[i] > mx) {
19             id = i;
20             mx = i + p[i];
21         }
22     }
23 }
24 
25 int main() {
26     scanf("%d", &T);
27     while(T--) {
28         scanf("%d", &n);
29         cnt = 0;
30         s[cnt++] = -2; s[cnt++] = -1;
31         for(int i = 0; i < n; ++i) {
32             scanf("%d", &s[cnt++]);
33             s[cnt++] = -1;
34         }
35         s[cnt] = 0;
36         manacher();
37         int ans = 0;
38         for(int i = 0; i < cnt; ++i)
39             ans = max(ans, p[i] - 1);
40         printf("%d\n", ans);
41     }
42 }