HDU 5791 Two (dp)

 1 //#pragma comment(linker, "/STACK:102400000, 102400000")
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <cstdlib>
 5 #include <cstring>
 6 #include <cstdio>
 7 #include <vector>
 8 #include <cmath>
 9 #include <ctime>
10 #include <list>
11 #include <set>
12 #include <map>
13 using namespace std;
14 typedef long long LL;
15 typedef pair <int, int> P;
16 const int N = 1e3 + 5;
17 //dp[i][j]表示a[i]b[j]之前的所有相同的自序列个数
18 //cnt[i][j]表示当a[i] == b[j]时以a[i]结尾的相同子序列个数
19 LL dp[N][N], cnt[N][N];
20 LL a[N], b[N];
21 LL mod = 1e9+7;
22 int main()
23 {
24     int n, m;
25     while(~scanf("%d %d", &n, &m)) {
26         for(int i = 1; i <= n; ++i)
27             scanf("%lld", a + i);
28         for(int i = 1; i <= m; ++i)
29             scanf("%lld", b + i);
30         memset(dp, 0, sizeof(dp));
31         memset(cnt, 0, sizeof(cnt));
32         for(int i = 1; i <= n; ++i) {
33             for(int j = 1; j <= m; ++j) {
34                 if(a[i] == b[j])
35                     cnt[i][j] = (dp[i - 1][j - 1] + 1) % mod;
36                 dp[i][j] = ((dp[i][j - 1] + dp[i - 1][j] - dp[i - 1][j - 1]) % mod + cnt[i][j]) % mod;
37             }
38         }
39         printf("%lld\n", (dp[n][m] + mod) % mod);
40     }
41     return 0;
42 }