hdoj3652 B-number

题意：给出n，问1-n中有13且能整除13的数数量。

就是hd3555和codeforces beautiful number的合成版。dp记录待填长度，是否带有13，前面数的模13余数，前一个数是k的时候的b-number数数量。

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cstring>
#include <map>
#include <queue>
#include <set>
#include <cassert>
using namespace std;
const double EPS=1e-8;
const int SZ=5050,INF=0x7FFFFFFF;
typedef long long lon;
int dp[20][15][10][2];

int dfs(int pos,int sum,int pre,int limit,string &str,int inc)
{
    if(pos==str.size())return inc&&(sum%13==0);
    if(!limit&&dp[str.size()-pos-1][sum][pre][inc]!=-1)return dp[str.size()-pos-1][sum][pre][inc];
    int up=limit?str[pos]-'0':9;
    int res=0;
    for(int i=0;i<=up;++i)
    {
        int nexsum=(sum*10+i)%13;
        if(pre==1&&i==3)res+=dfs(pos+1,nexsum,i,limit&&i==str[pos]-'0',str,1);
        else res+=dfs(pos+1,nexsum,i,limit&&i==str[pos]-'0',str,inc);
        //if(pos==1&&pre==1)cout<<i<<" "<<res<<" "<<endl;
    }
    if(!limit)dp[str.size()-pos-1][sum][pre][inc]=res;
    return res;
}

int work(string &str)
{
    return dfs(0,0,0,1,str,0);
}

int main()
{
    std::ios::sync_with_stdio(0);
    //freopen("d:\\1.txt","r",stdin);
    //lon casenum;
    //cin>>casenum;
    memset(dp,-1,sizeof(dp));
    //for(lon time=1;time<=casenum;++time)
    string str;
    for(lon time=1;cin>>str;++time)
    {
        cout<<work(str)<<endl;
    }
    return 0;
}