不错的dp
long long 果然比int慢好多
#include<cstdio> #include<cstring> #include<vector> #include<cmath> #include<algorithm> #define N 1010 #define mod 1000000007 using namespace std; typedef long long ll; int sum[N][N]; char s[1010]; int main(){ int i,j,n; while(scanf("%s",&s)==1){ n=strlen(s)+1; memset(sum,0,sizeof(sum)); sum[1][1]=1; for(i=2;i<=n;i++){ for(j=1;j<=i;j++){ if(s[i-2]=='I' || s[i-2]=='?') sum[i][j]=sum[i-1][j-1]; if(s[i-2]=='D' || s[i-2]=='?') sum[i][j]=((sum[i][j]+sum[i-1][i-1]-sum[i-1][j-1])%mod+mod)%mod; sum[i][j]=(sum[i][j]+sum[i][j-1])%mod; } } printf("%d\n",sum[n][n]); } }
可参考(http://blog.csdn.net/shiqi_614/article/details/7983298)