FZU 2170 花生的序列

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define MOD 1000000007
int dp[3010],v[3010];
char str[6010];
int main()
{

    int t,i,j;
    int n;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        scanf("%s",str+1);
        dp[0] = 1;
        v[0] = 1;
        for(i=0; i<=n; i++)
            for (j=0; j<=n; j++)
            {
                if(i==0 && j==0) continue;
                int sum = 0;
                if(str[i+j] == ‘W‘)
                {
                    if(i&1)
                        sum = (sum+v[j]) % MOD;
                    if(j&1)
                        sum = (sum+dp[j-1]) % MOD;

                    v[j] = dp[j] = sum % MOD;
                }
                else
                {
                    if(i>0 && (i&1)==0)
                        sum = (sum+v[j]) % MOD;
                    if(j>0 && (j&1)==0)
                        sum = (sum + dp[j-1]) % MOD;

                    v[j] = dp[j] = sum % MOD;
                }
            }
        printf("%d\n",dp[n]);
    }
    return 0;
}