HDU 4507 —— 吉哥系列故事――恨7不成妻

#include <cstdio>
#include <iostream>
#include <cstring>
#include <string>
using namespace std;

typedef long long LL;

struct P{
    LL num, sum, sqrt;
    P(LL a=-1, LL b=0, LL c=0):num(a),sum(b),sqrt(c){}
};

const int MOD = (int)1e9+7;
int a[20];
LL base[20];
P dp[20][7][7];


P dfs(int len, int mod1, int mod2, bool limit)
{
    if(len < 1)    
        return P(mod1 != 0 && mod2 != 0, 0, 0);
        
    if(!limit && dp[len][mod1][mod2].num!=-1)    return dp[len][mod1][mod2];
    int maxn = limit ? a[len] : 9;
    P ret(0,0,0);
    for(int i=0; i<=maxn; i++) {
        if(i==7)    continue;
        P cur = dfs(len-1, (mod1+i%7)%7, (mod2*(10%7)+i)%7, limit&&i==maxn);
        ret.num = (ret.num + cur.num) % MOD;
        ret.sum = (ret.sum + cur.sum + i * base[len] % MOD * cur.num % MOD) % MOD;
        LL temp = i*base[len]%MOD;
        ret.sqrt = (ret.sqrt + cur.sqrt + cur.num*temp%MOD*temp%MOD + 2*temp%MOD*cur.sum%MOD)%MOD;
    }
    if(!limit)    dp[len][mod1][mod2] = ret;
    return ret;
}

LL f(LL x)
{
    int len = 0;
    while(x) {
        a[++len] = x%10;
        x /= 10;
    }
    return dfs(len, 0, 0, 1).sqrt;
}

void Init()
{
    base[1]=1;
    for(int i=2; i<20; i++) {
        base[i] = base[i-1]*10;
//        printf("%lld\n", base[i]); //
    }    
}

int main ()
{
    Init();
    
    int T;
    LL l, r;
    scanf("%d", &T);
    while(T--) {
        scanf("%I64d%I64d", &l, &r);
        printf("%I64d\n", (f(r) - f(l-1) + MOD) % MOD);
    }
    
    return 0;
}