【数位DP】恨7不成妻

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 const ll mod=1e9+7;
 5 ll l,r,decimal[25],a[25];
 6 struct node
 7 {
 8     ll sum0,sum1,sum2;
 9     node():sum0(0),sum1(0),sum2(0) {}
10 }dp[25][10][10];
11 node dfs(int pos,int addremain,int numremain,bool limit)
12 {
13     if(pos==0)
14     {
15         node cnt;
16         if(addremain && numremain) cnt.sum0=1;
17         return cnt;
18     }
19     if(dp[pos][addremain][numremain].sum0 && !limit) return dp[pos][addremain][numremain];
20     node res;
21     ll up=limit?a[pos]:9;
22     for(ll i=0;i<=up;i++)
23     {
24         if(i==7) continue;
25         node tmp=dfs(pos-1,(addremain+i)%7,(numremain*10+i)%7,i==a[pos]&&limit);
26         res.sum0=(res.sum0+tmp.sum0)%mod;
27         res.sum1=(res.sum1+tmp.sum1+decimal[pos-1]*i%mod*tmp.sum0%mod)%mod;
28         res.sum2=(res.sum2+tmp.sum2+2*i%mod*decimal[pos-1]%mod*tmp.sum1%mod
29                   +i*i%mod*decimal[pos-1]%mod*decimal[pos-1]%mod*tmp.sum0%mod)%mod;
30     }
31     if(!limit) dp[pos][addremain][numremain]=res;
32     return res;
33 }
34 ll solve(ll val)
35 {
36     int len=0;
37     while(val)
38     {
39        a[++len]=val%10;
40        val/=10;
41     }
42     return dfs(len,0,0,true).sum2;
43 }
44 int main()
45 {
46     decimal[0]=1;
47     for(int i=1;i<=20;i++) decimal[i]=decimal[i-1]*10%mod;
48     int t;
49     for(scanf("%d",&t);t;t--)
50     {
51         scanf("%lld %lld",&l,&r);
52         printf("%lld\n",(solve(r)-solve(l-1)+mod)%mod);
53     }
54     return 0;
55 }
56 //1 1000000000000000000