B-number (数位dp入门)

题目链接

n中存在“13”且n%13==0
注意参数ok的状态转移

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int mod = 13;
int len,dig[20];
ll dp[20][20][2][20];
ll dfs(int pos,int prev,int ok,int remain,bool limit){
    if(pos==0){
        if(remain%13==0) return ok;
        return 0;
    }
    if(!limit&&dp[pos][prev][ok][remain]!=-1) return dp[pos][prev][ok][remain];
    int i;
    int up = limit?dig[pos]:9;
    ll ans = 0;
    for(i = 0;i <= up;i ++){
        if(prev==1&&i==3) ans += dfs(pos-1,i,1,(remain*10+i)%mod,limit&&i==up);
        else ans += dfs(pos-1,i,ok,(remain*10+i)%mod,limit&&i==up);
    }
    if(!limit) dp[pos][prev][ok][remain] = ans;
    return ans;
}
ll solve(ll n){
    len = 0;
    while(n!=0){
        dig[++len] = n%10;
        n /= 10;
    }
    return dfs(len,0,0,0,1);
}
int main()
{
   // freopen("a.txt","r",stdin);
    memset(dp,-1,sizeof(dp));
    ll l,r;
    while(cin>>r){
        l = 1;
        cout<<solve(r)-solve(l-1)<<endl;
    }
    return 0;
}