hdu 4906 Our happy ending
Our happy ending
Time Limit: 6000/3000 MS (Java/Others) Memory Limit: 131072/131072 K (Java/Others)Total Submission(s): 700 Accepted Submission(s): 223
Problem Description
There is an old country and the king fell in love with a devil. The devil always asks the king to do some crazy things. Although the king used to be wise and beloved by his people. Now he is just like a boy in love and can’t refuse any request from the devil. Also, this devil is looking like a very cute Loli.
Y*wan still remember the day he first meets the devil. Now everything is done and the devil is gone. Y*wan feel very sad and suicide.
You feel guilty after killing so many loli, so you suicide too.
Nobody survive in this silly story, but there is still some hope, because this is just a silly background story during one programming contest!
And the last problem is:
Given a sequence a_1,a_2,...,a_n, if we can take some of them(each a_i can only be used once), and they sum to k, then we say this sequence is a good sequence.
How many good sequence are there? Given that each a_i is an integer and 0<= a_i <= L.
You should output the result modulo 10^9+7.
Y*wan still remember the day he first meets the devil. Now everything is done and the devil is gone. Y*wan feel very sad and suicide.
You feel guilty after killing so many loli, so you suicide too.
Nobody survive in this silly story, but there is still some hope, because this is just a silly background story during one programming contest!
And the last problem is:
Given a sequence a_1,a_2,...,a_n, if we can take some of them(each a_i can only be used once), and they sum to k, then we say this sequence is a good sequence.
How many good sequence are there? Given that each a_i is an integer and 0<= a_i <= L.
You should output the result modulo 10^9+7.
Input
The first line contains an integer T, denoting the number of the test cases.
For each test case, the first line contains 3 integers n, k, L.
T<=20, n,k<=20 , 0<=L<=10^9.
For each test case, the first line contains 3 integers n, k, L.
T<=20, n,k<=20 , 0<=L<=10^9.
Output
For each cases, output the answer in a single line.
Sample Input
1 2 2 2
Sample Output
6
Author
WJMZBMR
题意：给你n个数字，每个数字可以是1~L，要求取几个数，使他们的和为k，求方案数
思路：状态压缩。dp[i]表示i这个状态的方法数，使用滚动数组，像背包那样从后往前递推防MLE。
状态转移：令k = 4 ，s = (1<<4) - 1 = 1111(2). 令前一状态为1010（表示能构成2，4的方法数），若当前取1，则下一状态为能构成1，3的方法数（即1,1+2,1+4（去掉））。
所以next = i | ((i< 对于那些超出K的数，它们都转移会自己。 代码如下：#include
#include