hdu 5396 Expression

太弱经常暴露智商.....

最近刷的个个dp都是区间，记忆化搜索也区间

然而窝组合数递推不会，规律推错了也不造，orz~~~

这题就找个规律，直接记忆化搜索干就是了，没什么难得

贴一发丑丑的代码，匿了

#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
",(dp[1][n]+mod)%mod);
    }
    return 0;
}