题目描述
We are given a sequence of n decimal digits. The sequence needs to be partitioned into one or more contiguous subsequences such that each subsequence, when interpreted as a decimal number, is divisible by a given integer m.
Find the number of different such partitions modulo 10^9 +7. When determining if two partitions are different, we only consider the locations of subsequence boundaries rather than the digits themselves, e.g. partitions 2|22 and 22|2 are considered different.
输入输出格式
输入格式：
The ?rst line contains two integers n and m (1≤n≤300000, 1≤m≤1000000) – the length of the sequence and the divisor respectively. The second line contains a string consisting of exactly n digits.
输出格式：
Output a single integer – the number of different partitions modulo 109 +7.
输入输出样例
说明
Central Europe Regional Contest 2015 Problem D
我们发现分出来的每段的末尾i 的前缀数字 s[i] 都必须是 m的倍数， 否则中间肯定有一段%m!=0(想一想为什么)，然后这就是个SB题了233
#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int ha=1000000007;
int n,m,T,num;
char ch;
inline int add(int x,int y){
x+=y;
return x>=ha?x-ha:x;
}
inline int C(int y){
int an=1,x=2;
for(;y;y>>=1,x=x*(ll)x%ha) if(y&1) an=an*(ll)x%ha;
return an;
}
int main(){
scanf("%d%d",&n,&m);
const int M=m;
for(int i=1;i<=n;i++){
ch=getchar();
while(!isdigit(ch)) ch=getchar();
num=((num*10)+ch-‘0‘)%M;
if(!num) T++;
}
if(num) puts("0");
else printf("%d\n",C(T-1));
return 0;
}