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
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
|
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<stack>
#include<cmath>
#include<set>
#include<bitset>
#include<complex>
#include<cstdlib>
#include<assert.h>
#define inc(i,l,r) for(int i=l;i<=r;i++)
#define dec(i,l,r) for(int i=l;i>=r;i--)
#define link(x) for(edge *j=h[x];j;j=j->next)
#define mem(a) memset(a,0,sizeof(a))
#define ll long long
#define eps 1e-8
#define succ(x) (1<<x)
#define lowbit(x) (x&(-x))
#define mid (x+y>>1)
#define sqr(x) ((x)*(x))
#define NM 5005
#define nm 2097152
using namespace std;
const double pi=acos(-1);
const ll inf=1e9+7;
ll read(){
ll x=0,f=1;char ch=getchar();
while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
while(isdigit(ch))x=x*10+ch-'0',ch=getchar();
return f*x;
}
inline ll qpow(ll x,ll t){
ll s=1;
for(;t;t>>=1,x=x*x%inf)if(t&1)s=s*x%inf;
return s;
}
int n;
ll _t,d[NM][NM],g[NM][NM],ans;
char _s[NM];
int main(){
n=read();_t=read();_t=_t*qpow(read()+_t,inf-2)%inf;
scanf("%s",_s+1);
g[n+1][read()]=1;d[0][read()]=1;
inc(i,1,n)if(_s[i]=='H'){
inc(j,0,n)d[i][j]=d[i-1][j+1];
}else{
inc(j,1,n)d[i][j]=(d[i-1][j]*_t+d[i][j-1]*(inf+1-_t))%inf;
}
dec(i,n,1)if(_s[i]=='R'){
inc(j,0,n)g[i][j]=g[i+1][j+1];
}else{
inc(j,1,n)g[i][j]=(g[i+1][j]*(inf+1-_t)+g[i][j-1]*_t)%inf;
}
inc(i,0,n)ans+=d[i][0]*g[i+1][0],ans%=inf;
printf("%lld\n",ans);
return 0;
}
|
