bzoj 4521 [Cqoi2016]手机号码——数位dp

题目：https://www.lydsy.com/JudgeOnline/problem.php?id=4521

dfs真好用~

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define ll long long
using namespace std;
const int N=;
int dg[N];
ll l,r,dp[N][][N][][][];
ll dfs(int p,int len,int lst,bool p0,bool p1,bool ok,bool fx)
{
    if(!p){return ok&(!(p0&p1));}
    if(!fx&&dp[p][len][lst][p0][p1][ok]!=-)return dp[p][len][lst][p0][p1][ok];
    int st=;if(p==)st=;
    int end=;if(fx)end=dg[p];
    ll ret=;
    for(int i=st;i<=end;i++)
    {
        int lenn=;if(i==lst)lenn=len+;
        if(lenn>)lenn=;
        ret+=dfs(p-,lenn,i,p0|(i==),p1|(i==),ok|(lenn==),fx&(i==dg[p]));
    }
    if(!fx)dp[p][len][lst][p0][p1][ok]=ret;
    return ret;
}
ll calc(ll x)
{
    if(x<1e10)return ;
    for(int i=;i<=;i++)dg[i]=x%,x/=;
    memset(dp,-,sizeof dp);
    return dfs(,,,,,,);
}
int main()
{
    scanf("%lld%lld",&l,&r);
    printf("%lld\n",calc(r)-calc(l-));
    return ;
}