【HDOJ】4513 吉哥系列故事——完美队形II

这题目上学期就看了，不过最近发现可以用马拉车来解，而且还是基本算法。 稍微对回文串成立条件变形一下即可。

 /* 4513 */
 #include <iostream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 #include <iterator>
 #include <iomanip>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const int maxn = 1e5+;
 int a[maxn], b[maxn*];
 int Len[maxn*];

 void init(int n) {
     int j = ;

     b[j++] = -;
     b[j++] = ;
     rep(i, , n) {
         b[j++] = a[i];
         b[j++] = ;
     }
 }

 void manacher(int m) {
     int n = *m+;
     int p = , p0 = ;
     int lid, rid;

     rep(i, , n+) {
         if (p > i)
             Len[i] = min(p-i, Len[*p0-i]);
         else
             Len[i] = ;

         while (b[i+Len[i]] == b[i-Len[i]]) {
             if (b[i+Len[i]] > ) {
                 lid = i - Len[i];
                 rid = i + Len[i];
                 if (b[lid]>b[lid+] || b[rid]>b[rid-])
                     break;
             }
             ++Len[i];
         }

         if (i+Len[i] > p) {
             p = i + Len[i];
             p0 = i;
         }
     }
 }

 void solve(int n) {
     init(n);
     manacher(n);

     int ans = ;

     n = n*+;
     rep(i, , n) {
         ans = max(ans, Len[i]);
     }
     printf("%d\n", ans-);
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     int t;
     int n;

     scanf("%d", &t);
     while (t--) {
         scanf("%d", &n);
         rep(i, , n)
             scanf("%d", &a[i]);
         solve(n);
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }