hdu 4055 动态规划

#include<map>

#include<set>

#include<cmath>

#include<queue>

#include<cstdio>

#include<vector>

#include<string>

#include<cstdlib>

#include<cstring>

#include<iostream>

#include<algorithm>

#define Maxn 1010

#define Maxm 100010

#define LL __int64

#define Abs(x) ((x)>0?(x):(-x))

#define lson(x) (x<<1)

#define rson(x) (x<<1|1)

#define inf 0x7fffffff

#define Mod 1000000007

using namespace std;

int dp[Maxn][Maxn],sum[Maxn][Maxn];

char str[Maxn];

int main()

{

    int i,j,n;

    while(scanf("%s",str+2)!=EOF){

        memset(dp,0,sizeof(dp));

        dp[1][1]=1;

        sum[1][1]=1;

        n=strlen(str+2);

        for(i=2;i<=n+1;i++){

            if(str[i]=='I'||str[i]=='?'){

                for(j=1;j<=i;j++){

                    dp[i][j]+=(sum[i-1][j-1])%Mod;

                    dp[i][j]%=Mod;

                    sum[i][j]=sum[i][j-1]%Mod+dp[i][j]%Mod;

                    sum[i][j]%=Mod;

                }

            }

            if(str[i]=='D'||str[i]=='?')

            {

                for(j=1;j<=i;j++){

                    dp[i][j]+=(sum[i-1][i-1]%Mod-sum[i-1][j-1]%Mod+Mod)%Mod;

                    dp[i][j]%=Mod;

                    sum[i][j]=sum[i][j-1]%Mod+dp[i][j]%Mod;

                    sum[i][j]%=Mod;

                }

            }

        }

        int ans=0;

        for(i=1;i<=n+1;i++){

            ans+=dp[n+1][i];

            ans%=Mod;

        }

        printf("%d\n",ans);

    }

    return 0;

}