B. Yet Another Meme Problem (math)

题目

a * b+a+b=a * 10^n+b
a * b+a=a*10^n
b+1=10^n
故b=9 99 999 9999…
都满足情况，答案为a的个数乘1 —B中满足条件的b的数目

#include<iostream>
#include<cmath>
using namespace std;
typedef long long ll;
const int Max = 1e6 + 5;
ll a[Max], b[Max], lst[Max];

int main()
{
   
	int t;cin >> t;
	while (t--)
	{
   
		ll a, d;cin >> a >> d;
		ll num = -1, ans = 0;
		while (d>=ans)
		{
   
			ans = 9 + ans * 10;
			num++;
		}
		cout << a * num << endl;
	}
}