Two
题目链接：
http://acm.hdu.edu.cn/showproblem.php?pid=5791
Description
Alice gets two sequences A and B. A easy problem comes. How many pair of sequence A' and sequence B' are same. For example, {1,2} and {1,2} are same. {1,2,4} and {1,4,2} are not same. A' is a subsequence of A. B' is a subsequence of B. The subsequnce can be not continuous. For example, {1,1,2} has 7 subsequences {1},{1},{2},{1,1},{1,2},{1,2},{1,1,2}. The answer can be very large. Output the answer mod 1000000007.
Input
The input contains multiple test cases.
For each test case, the first line cantains two integers N,M(1≤N,M≤1000). The next line contains N integers. The next line followed M integers. All integers are between 1 and 1000.
Output
For each test case, output the answer mod 1000000007.
Sample Input
3 2
1 2 3
2 1
3 2
1 2 3
1 2
Sample Output
2
3
Source
2016 Multi-University Training Contest 5
##题意： 求A和B中有多少对子集完全相同.
##题解： 动态规划. dp[i][j]：分别处理到ij时ai==bj且用上ai bj后的对数. (ai!=bj时dp=0) 前缀和优化： sum[i][j]：分别处理到ij时满足条件的子集对数. (不一定用上ai bj)
状态转移： dp[i][j] = sum[i-1][j-1] + 1; 用上ai bj后的对数为ij之前的任意子集对再加上(ai, bj)这对子集. sum[i][j] = dp[i][j] + (sum[i][j-1] + sum[i-1][j] - sum[i-1][j-1]); 前缀和由当前满足条件的对数 + 之前满足条件的对数而来(去重).
##代码： ``` cpp #include