hdu 3709 Balanced Number(数位dp)

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
#define ll long long int
using namespace std;
inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
inline ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
int moth[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
int dir[2][2]={1,0 ,0,1};
int dirs[8][2]={1,0 ,0,1 ,-1,0 ,0,-1, -1,-1 ,-1,1 ,1,-1 ,1,1};
const int inf=0x3f3f3f3f;
int bits[20];
ll dp[20][20][2000]; //位数 平衡点位置  左右两边的和的差 
ll dfs(int len,int pos,int sum,bool ismax){
    if(!len) return sum==0; //如果左右相加为0就是平衡数 
    if(sum<0) return 0; //剪枝 
    if(!ismax&&dp[len][pos][sum]>=0) return dp[len][pos][sum];
    int up=ismax?bits[len]:9;
    ll cnt=0;
    for(int i=0;i<=up;i++){
        cnt+=dfs(len-1,pos,sum+(len-pos)*i,ismax&&i==up);
    }
    if(!ismax) dp[len][pos][sum]=cnt;
    return cnt;
}
ll solve(ll x){
    int len=0;
    while(x){
        bits[++len]=x%10;
        x/=10;
    }
    ll ans=0;
    for(int i=1;i<=len;i++){ //枚举分割点 
        ans+=dfs(len,i,0,true);
    }
    return ans-len-1;
}
int main(){
    ios::sync_with_stdio(false);
    int t;
    cin>>t;
    memset(dp,-1,sizeof(dp));
    while(t--){
        ll x,y; cin>>x>>y;
        cout<<solve(y)-solve(x-1)<<endl;
    }
    return 0;
}