手打AC的第2道数位DP：BZOJ1799: [Ahoi2009]self 同类分布

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

ll dp[20][180][180],n,m,a[1005];
ll dfs(int pos,int sum,int val,int mod,int limit){
    if (sum-9*(pos+1)>0) return 0;
    if (pos==0) return sum==0 && val==0;
    if (!limit && dp[pos][sum][val]!=-1) return dp[pos][sum][val];
    int up=limit?a[pos]:9;
    ll ans=0;
    for (int i=0; i<=up; i++)
    {
        if (sum-i<0) break;
        ans+=dfs(pos-1,sum-i,(val*10+i)%mod,mod,limit && a[pos]==i);
    }
    if (!limit) dp[pos][sum][val]=ans;
    return ans;
}

ll solve(ll x){
    ll pos=0;
    while (x){
        a[++pos]=x%10;
        x/=10;
    }
    ll ans=0;
    for (int i=1; i<=pos*9; i++)
    {
        memset(dp,-1,sizeof(dp));
        ans+=dfs(pos,i,0,i,1);
    }
    return ans;
}

int main(){
    scanf("%lld%lld",&n,&m);
    printf("%lld",solve(m)-solve(n-1));
    return 0;
}