Codeforces 595 B. Pasha and Phone【数学】
B. Pasha and Phone
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
Pasha has recently bought a new phone jPager and started adding his friends' phone numbers there. Each phone number consists of exactly n digits.
Also Pasha has a number k and two sequences of length n / k (n is divisible by k) a1, a2, ..., an / k and b1, b2, ..., bn / k. Let's split the phone number into blocks of length k. The first block will be formed by digits from the phone number that are on positions 1, 2,..., k, the second block will be formed by digits from the phone number that are on positions k + 1, k + 2, ..., 2·k and so on. Pasha considers a phone number good, if the i-th block doesn't start from the digit bi and is divisible by ai if represented as an integer.
To represent the block of length k as an integer, let's write it out as a sequence c1, c2,...,ck. Then the integer is calculated as the result of the expression c1·10k - 1 + c2·10k - 2 + ... + ck.
Pasha asks you to calculate the number of good phone numbers of length n, for the given k, ai and bi. As this number can be too big, print it modulo 109 + 7.
Input
The first line of the input contains two integers n and k (1 ≤ n ≤ 100 000, 1 ≤ k ≤ min(n, 9)) — the length of all phone numbers and the length of each block, respectively. It is guaranteed that n is divisible by k.
The second line of the input contains n / k space-separated positive integers — sequence a1, a2, ..., an / k (1 ≤ ai < 10k).
The third line of the input contains n / k space-separated positive integers — sequence b1, b2, ..., bn / k (0 ≤ bi ≤ 9).
Output
Print a single integer — the number of good phone numbers of length n modulo 109 + 7.
Examples
Input
6 2
38 56 49
7 3 4
Output
8
Input
8 2
1 22 3 44
5 4 3 2
Output
32400
Note
In the first test sample good phone numbers are: 000000, 000098, 005600, 005698, 380000, 380098, 385600, 385698.
给你一个电话号长度n，再给你一个数k，表示要将电话号分成n/k部分。每一部分长度为10^k。
而且每一部分必须是ai的倍数，并且不能以bi开头不足10^k长度的部分，前补0。
问你能够找到多少种可行方案。
思路：
1、首先我们知道，假如让我们求100以内3的倍数的个数，那么就是100/3；
2、那么我们设定c【i】表示区间范围（10^k）内有多少个a【i】的倍数，并且设定d【i】表示区间范围内去除的以b【i】开头的数字的个数。那么ans【i】=c【i】-d【i】；最后累乘ans【i】即可。
3、那么两个数组的求法：
c【i】=（10^k-1）/a【i】+1（+1是表示加全是0的这种情况）。
d【i】=（（b【i】+1）*(10^(k-1))-1）/a【i】-（b【i】*(10^(k-1))-1）/a【i】
注意，当b【i】==0的时候要特殊判定。
Ac代码：
#include
#include
using namespace std;
#define ll __int64
ll a[100002];
ll b[100002];
ll c[100002];
ll d[100002];
ll mod=1e9+7;
int main()
{
int n,k;
while(~scanf("%d%d",&n,&k))
{
int tmp=n/k;
int len=n/tmp;
ll qujian=1;
for(int i=1;i<=len;i++)
{
qujian*=10;
}
for(int i=0;i