# Common Subsequence

Jun 17th, 2019
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1. #include <bits/stdc++.h>
2. using namespace std;
3. #define PB push_back
4. #define ZERO (1e-10)
5. #define INF int(1e9+1)
6. #define CL(A,I) (memset(A,I,sizeof(A)))
7. #define DEB printf("DEB!\n");
8. #define D(X) cout<<"  "<<#X": "<<X<<endl;
9. #define EQ(A,B) (A+ZERO>B&&A-ZERO<B)
10. typedef long long ll;
11. typedef pair<ll,ll> pll;
12. typedef vector<int> vi;
13. typedef pair<int,int> ii;
14. typedef vector<ii> vii;
15. #define IN(n) int n;scanf("%d",&n);
16. #define FOR(i, m, n) for (int i(m); i < n; i++)
17. #define F(n) FOR(i,0,n)
18. #define FF(n) FOR(j,0,n)
19. #define FT(m, n) FOR(k, m, n)
20. #define aa first
21. #define bb second
22. void ga(int N,int *A){F(N)scanf("%d",A+i);}
23. #define MOD 1000000007
24. #define MX 2048
25. int dp[MX][MX][2][2],N,M,A[MX],B[MX];
26. int dyn(int a,int b,bool x,bool y){
27.     if(a==N||b==M)return !x&&!y;
28.     int&v=dp[a][b][x][y];
29.     if(~v)return v;
30.     v=0;
31.     if(A[a]==B[b])v=dyn(a+1,b+1,0,0);
32.     if(!x&&!y)v=(v+dyn(a+1,b+1,0,0))%MOD;
33.     if(x)v=(v+dyn(a,b+1,1,0))%MOD;
34.     if(y)v=(v+dyn(a+1,b,0,1))%MOD;
35.     if(!x&&!y)v=(v+ll(dyn(a+1,b,0,1))+dyn(a,b+1,1,0))%MOD;
36.     return v;
37. }
38. int main(void){
39.     scanf("%d%d",&N,&M),ga(N,A),ga(M,B),CL(dp,-1);
40.     printf("%d\n",dyn(0,0,0,0));
41.     return 0;
42. }