Meaning of the questions:
To a string (by the numeral '0' - '9' composition), a prime number p, and asked how many non-empty string is a multiple of p
Ideas:
to record the current value x mod p if x is equal to the front there are several, to add a few, because the string mod p == 0 among them any one of these to the current location
p = 2 || p = 5, as long as the mod p == 0, the multiple places to end of the string is p
Code:
#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <vector>
#include <math.h>
#include <map>
#include <queue>
#include <set>
#include <stack>
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define per(i,a,b) for(int i=a;i>=b;i--)
typedef long long ll;
using namespace std;
const int MAXN=2e5+50;
const int inf=0x3f3f3f3f;
const int M=5000*4;
char ch[MAXN];
int cnt[MAXN];
int main()
{
int n,p;
cin>>n>>p;
cin>>(ch+1);
ll ans=0;
if(p==2||p==5){
for(int i=1;i<=n;i++){
if((ch[i]-'0')%p==0)ans+=i;
}
cout<<ans<<endl;
return 0;
}
int t=1,x=0;
cnt[0]=1;
for(int i=n;i>=1;i--){
x=(x+(ch[i]-'0')*t)%p;
ans+=cnt[x];
cnt[x]++;
t=t*10%p;
}
cout<<ans<<endl;
return 0;
}
/*
*/
A similar title 2019 cattle off summer school and more training camp (fourth) K number (thinking)
