rt,如何优化本代码？

#include<cstdio>
#include<string>
using namespace std;
typedef long long in;
int t,n,i,x=1,y=1,z,b[1000010]={0,1,2};
int fg(int x){
	string s=to_string(x);
	int i,sum=0;
	for(i=0;i<s.size();++i)sum+=s[i]-'0';
	return sum;
}int main(){
	for(i=3;i<=1000000;++i){
		z=x+y;
		x=y;
		y=fg(z);
		b[i]+=b[i-1]+y;
	}scanf("%d",&t);
	while(t--){
		scanf("%d",&n);
		printf("%d\n",b[n]%9);
	}return 0;
}