Codeforces 628D Magic Numbers [디지털 dp]

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define CLR(a, b) memset(a, (b), sizeof(a))
#define PI acos(-1.0)
using namespace std;
typedef long long LL;
typedef double DD;
const int MAXN = 1e5+10;
const int MOD = 1e9+7;
int m, d, L;
int bit[2001];
LL dp[2001][2001];
void add(LL &x, LL y) {x = (x + y) % MOD;}
LL DFS(int pos, int preyu, bool yes)
{
    if(pos == L) return preyu == 0;
    if(!yes && dp[pos][preyu] != -1) return dp[pos][preyu];
    LL ans = 0;
    int End = yes ? bit[pos] : 9;
    for(int i = 0; i <= End; i++)
    {
        if(pos % 2 == 0 && i == d) continue;
        if(pos % 2 == 1 && i != d) continue;
        add(ans, DFS(pos+1, (preyu*10+i)%m, yes&&i==End));
    }
    if(!yes) dp[pos][preyu] = ans;
    return ans;
}
LL Count(string str)
{
    int len = str.size(); int cnt = 0;
    for(int i = 0; i < len; i++) bit[i] = str[i] - '0';
    return DFS(0, 0, 1);
}
bool judge(string str)
{
    int len = str.size(); int yu = 0;
    for(int i = 0; i < len; i++)
    {
        int v = str[i] - '0';
        yu = yu * 10 + v; yu %= m;
        if((i + 1) & 1 && v == d) return false;
        if(i & 1 && v != d) return false;
    }
    return yu == 0;
}
int main()
{
    CLR(dp, -1);
    cin >> m >> d;
    string a, b; cin >> a >> b; L = a.size();
    //cout << judge(a) << ' ';
    cout << (Count(b) - Count(a) + judge(a) + MOD) % MOD << endl;
    return 0;
}