hdu 5396 Expression

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define ll __int64
const int mod=1e9+7;
const int maxn=108;
int a[maxn];
char b[maxn];
ll dp[maxn][maxn];
ll pig[maxn][maxn],jie[maxn];
void init()
{
int i,j;
for(i=0;i<=100;i++)
{
pig[i][0]=pig[i][i]=1;
for(j=1;j<i;j++)
pig[i][j]=(pig[i-1][j]+pig[i-1][j-1])%mod;
}
}
void initjie()
{
jie[0]=1;
for(int i=1;i<=100;i++)
jie[i]=jie[i-1]*i%mod;
}
void dfs(int l,int r)
{
int i;
if(dp[l][r]!=-1)    return;
if(l==r)
{
dp[l][r]=a[l];
return;
}
ll x,y,sum=0;
for(i=l;i<r;i++)
{
dfs(i+1,r);
dfs(l,i);
if(b[i-1]=='*')
{
if(i-l>=1&&r-i-1>=1)
{
sum=(sum+pig[r-l-1][i-l]*(dp[l][i]*dp[i+1][r]%mod))%mod;
}
else
sum=(sum+dp[l][i]*dp[i+1][r])%mod;
}
if(b[i-1]=='-')
{
if(i-l>=1&&r-i-1>=1)
{
sum=(sum+pig[r-l-1][i-l]*
((jie[r-i-1]*dp[l][i]-jie[i-l]*dp[i+1][r])%mod))%mod;
}
else
sum=(sum+jie[r-i-1]*dp[l][i]-jie[i-l]*dp[i+1][r])%mod;
}
if(b[i-1]=='+')
{
if(i-l>=1&&r-i-1>=1)
{
sum=(sum+pig[r-l-1][i-l]*
((jie[r-i-1]*dp[l][i]+jie[i-l]*dp[i+1][r])%mod))%mod;
}
else
sum=(sum+jie[r-i-1]*dp[l][i]+jie[i-l]*dp[i+1][r])%mod;
}
}
dp[l][r]=sum;
}
int main()
{
int i,j,n;
ll sum;
init();
initjie();
while(scanf("%d",&n)==1)
{
for(i=1;i<=n;i++)
scanf("%d",&a[i]);
scanf("%s",b);
memset(dp,-1,sizeof(dp));
dfs(1,n);
printf("%I64d\n",(dp[1]
+mod)%mod);
}
return 0;
}