# 数位DP入坑

Posted 2021-01-16 lovewhy

Hdu 2089 不要62

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;

typedef long long LL;

inline int read()
{
    char c=getchar();int num=0;
    for(;!isdigit(c);c=getchar());
    for(;isdigit(c);c=getchar())
        num=num*10+c-‘0‘;
    return num;
}

const int N=1e6+5;

int n,m;
int a[20],dgt;
int f[20][2;

int dfs(int dep,int pre,int sta,bool lim)
{
    if(!dep)
        return 1;
    if(!lim&&f[dep][sta!=-1)
        return f[dep][sta];
    int up=lim?a[dep]:9;
    int ans=0;
    for(int i=0;i<=up;++i)
    {
        if(i==4) continue;
        if(pre==6&&i==2) continue;
        ans+=dfs(dep-1,i,i==6,lim&&i==a[dep]);
    }
    if(!lim)
        f[dep][sta]=ans;
    return ans;
}

int solve(int x)
{
    for(dgt=0;x;a[++dgt]=x%10,x/=10);
    return dfs(dgt,0,0,1);
}

int main()
{
    while(1)
    {
        memset(f,-1,sizeof(f));
        n=read(),m=read();
        if(!n&&!m)
            break;
        cout<<solve(m)-solve(n-1)<<‘
‘;
    }
    return 0;
}

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Hdu 6148 Valley Numer

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;

typedef long long LL;

inline int read()
{
    char c=getchar();int num=0;
    for(;!isdigit(c);c=getchar());
    for(;isdigit(c);c=getchar())
        num=num*10+c-‘0‘;
    return num;
}

const int N=105;
const int mod=1e9+7;

int T,n;
char a[N];
int f[N][10][3];

int dfs(int dep,int pre,int turn,bool lim,bool invalid)
{
    if(dep==n+1)
        return invalid?0:1;
    if(!lim&&f[dep][pre][turn]!=-1)
        return f[dep][pre][turn];
    int up=lim?a[dep]-=‘0‘:9;
    int ans=0;
    for(int i=0;i<=up;++i)
    {
        if(turn==2&&i<pre)
            continue;
        int p=0;
        if(invalid) p=0;
        else if(i>pre) p=2;
        else if(i<pre) p=1;
        else p=turn;
        ans+=dfs(dep+1,i,p,lim&&i==a[dep],invalid&&i==0);
        ans%=mod;
    }
    if(!lim)
        f[dep][pre][turn]=ans;
    return ans;
}

int main()
{
    T=read();
    while(T--)
    {
        memset(f,-1,sizeof(f));
        scanf("%s",a+1);
        n=strlen(a+1);
        cout<<dfs(1,0,0,1,1)<<‘
‘;
    }
    return 0;
}

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