随笔 - 87  文章 - 279  trackbacks - 0
<2007年4月>
25262728293031
1234567
891011121314
15161718192021
22232425262728
293012345

潜心看书研究!

常用链接

留言簿(19)

随笔分类(81)

文章分类(89)

相册

ACM OJ

My friends

搜索

  •  

积分与排名

  • 积分 - 211780
  • 排名 - 116

最新评论

阅读排行榜

评论排行榜

PKU 3093 Margaritas on the River Walk
        先对输入的数组排序,然后类似于01对a[i]做决策,核心代码加了注释:
         for (i=1; i<=n; i++) {
                 for (j=1; j<=maxsum; j++) {
                        if (j >= sum[i]) d[i][j] = 1; //j比sum[i]大,肯定这时候d[i][j]=1;
                        else {
                                d[i][j] = d[i-1][j];//不考虑a[i]
                                if (j-a[i]>=0) {//考虑a[i]
                                         if (d[i-1][j-a[i]] > 0) d[i][j] += d[i-1][j-a[i]];//把a[i]加进以前的选择里面
                                         else d[i][j]++;//a[i]单独作为一个选择(这里需要先对a[i]排序,消除后效性)
                               }
                        }
                 }
         }

PKU 1037 A decorative fence
        先dp算出以i为起点的序列的个数,再组合数学
        td[n][i]和tu[n][i]分别表示个数为n,以i开始的上升和下降的序列个数
        易知:
        td[n][1] = 0;
        td[n][i] = sigma(tu[n-1][j], j从1..i-1)  = td[n][i-1] + tu[n-1][i-1] ;
        tu[n][i]  = td[n][n+i-1];

PKU 2677 Tour
        双调欧几里德旅行商问题(明显阶段dp)
        动态规划方程 :d[i+1][i] = mint(d[i+1][i], d[i][j]+g[j][i+1]); 
                                      d[i+1][j] = mint(d[i+1][j], d[i][j]+g[i][i+1]);
                                       0<=j<i   

PKU 2288 Islands and Bridges
        集合DP
        状态表示: d[i][j][k] (i为13为二进制表示点的状态, j为当前节点, k为到达j的前驱节点)

posted on 2007-04-20 18:10 阅读(2095) 评论(5)  编辑 收藏 引用 所属分类: 算法&ACM

FeedBack:
# re: 对一些DP题目的小结 2007-04-22 08:56 byron
豪大牛,问一下,这是一些题目吗????  回复  更多评论
  
# re: 对一些DP题目的小结 2007-04-24 00:52 
@byron
是pku上的题目,我菜菜啊。。。  回复  更多评论
  
# re: 对一些DP题目的小结 2007-04-26 18:59 oyjpart
呵呵 就聊上了啊 :)  回复  更多评论
  
# re: 对一些DP题目的小结 2007-06-30 22:55 姜雨生
Margaritas on the River Walk
Time Limit:1000MS Memory Limit:65536K
Total Submit:309 Accepted:132

Description


One of the more popular activities in San Antonio is to enjoy margaritas in the park along the river know as the River Walk. Margaritas may be purchased at many establishments along the River Walk from fancy hotels to Joe’s Taco and Margarita stand. (The problem is not to find out how Joe got a liquor license. That involves Texas politics and thus is much too difficult for an ACM contest problem.) The prices of the margaritas vary depending on the amount and quality of the ingredients and the ambience of the establishment. You have allocated a certain amount of money to sampling different margaritas.

Given the price of a single margarita (including applicable taxes and gratuities) at each of the various establishments and the amount allocated to sampling the margaritas, find out how many different maximal combinations, choosing at most one margarita from each establishment, you can purchase. A valid combination must have a total price no more than the allocated amount and the unused amount (allocated amount – total price) must be less than the price of any establishment that was not selected. (Otherwise you could add that establishment to the combination.)

For example, suppose you have $25 to spend and the prices (whole dollar amounts) are:

Vendor A B C D H J
Price 8 9 8 7 16 5

Then possible combinations (with their prices) are:

ABC(25), ABD(24), ABJ(22), ACD(23), ACJ(21), ADJ( 20), AH(24), BCD(24), BCJ(22), BDJ(21), BH(25), CDJ(20), CH(24), DH(23) and HJ(21).

Thus the total number of combinations is 15.


Input


The input begins with a line containing an integer value specifying the number of datasets that follow, N (1 ≤ N ≤ 1000). Each dataset starts with a line containing two integer values V and D representing the number of vendors (1 ≤ V ≤ 30) and the dollar amount to spend (1 ≤ D ≤ 1000) respectively. The two values will be separated by one or more spaces. The remainder of each dataset consists of one or more lines, each containing one or more integer values representing the cost of a margarita for each vendor. There will be a total of V cost values specified. The cost of a margarita is always at least one (1). Input values will be chosen so the result will fit in a 32 bit unsigned integer.


Output


For each problem instance, the output will be a single line containing the dataset number, followed by a single space and then the number of combinations for that problem instance.


Sample Input


2
6 25
8 9 8 7 16 5
30 250
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30

Sample Output


1 15
2 16509438

Hint


Note: Some solution methods for this problem may be exponential in the number of vendors. For these methods, the time limit may be exceeded on problem instances with a large number of vendors such as the second example below.


Source
Greater New York 2006
  回复  更多评论
  
# re: 对一些DP题目的小结 2007-06-30 22:59 姜雨生
应该可以更加优化  回复  更多评论
  

只有注册用户登录后才能发表评论。
网站导航: 博客园   IT新闻   BlogJava   知识库   博问   管理