LPS HDOJ 4745 Two Rabbits

 1 /*
 2     题意：一只兔子顺时针跳，另一只逆时针跳，跳石头权值相等而且不能越过起点
 3     LPS：这道就是LPS的应用，把环倍增成链，套一下LPS，然而并不能理解dp[i][i+n-2] + 1，看别人的解题报告吧，以后来补(玩游戏)
 4 　　详细解释 
 5 */
 6 /************************************************
 7 * Author        :Running_Time
 8 * Created Time  :2015-8-8 16:57:23
 9 * File Name     :HDOJ_4747_LPS.cpp
10  ************************************************/
11 
12 #include <cstdio>
13 #include <algorithm>
14 #include <iostream>
15 #include <sstream>
16 #include <cstring>
17 #include <cmath>
18 #include <string>
19 #include <vector>
20 #include <queue>
21 #include <deque>
22 #include <stack>
23 #include <list>
24 #include <map>
25 #include <set>
26 #include <bitset>
27 #include <cstdlib>
28 #include <ctime>
29 using namespace std;
30 
31 #define lson l, mid, rt << 1
32 #define rson mid + 1, r, rt << 1 | 1
33 typedef long long ll;
34 const int MAXN = 2e3 + 10;
35 const int INF = 0x3f3f3f3f;
36 const int MOD = 1e9 + 7;
37 int a[MAXN], dp[MAXN][MAXN];
38 
39 
40 int main(void)    {     //HDOJ 4745 Two Rabbits
41     int n;
42     while (scanf ("%d", &n) == 1)   {
43         if (!n) break;
44         for (int i=1; i<=n; ++i)    {
45             scanf ("%d", &a[i]);
46             a[i+n] = a[i];
47         }
48         memset (dp, 0, sizeof (dp));
49         for (int i=1; i<=2*n; ++i)  dp[i][i] = 1;
50         for (int i=2; i<2*n; ++i)    {
51             for (int j=1; j+i-1<=2*n; ++j)    {
52                 if (a[j] == a[j+i-1]) dp[j][j+i-1] = dp[j+1][j+i-2] + 2;
53                 else    {
54                     dp[j][j+i-1] = max (dp[j+1][j+i-1], dp[j][j+i-2]);
55                 }
56             }
57         }
58         int ans = 0;
59         for (int i=1; i<=n; ++i)    {
60             ans = max (ans, dp[i][i+n-1]);
61             ans = max (ans, dp[i][i+n-2] + 1);
62         }
63         printf ("%d
", ans);
64     }
65 
66     return 0;
67 }
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