C++ 代码

#include <bits/stdc++.h>
using namespace std;

const int N = 120;

int dp[N][N];
int arr[N];
int mod;

int dfs(int pos, long long sum, int limit){
    if(!pos) return (sum % mod) == 0;
    if(!limit && dp[pos][sum] != -1) return dp[pos][sum];
    int up = limit ? arr[pos] : 9;
    int ans = 0;
    for(int i = 0;i <= up;++i)
        ans += dfs(pos-1, sum + i, limit && (i == up));
    if(!limit) dp[pos][sum] = ans;
    return ans;
} 

int solve(int x){
    int cnt = 0;
    while(x) arr[++cnt] = x % 10, x /= 10;
    memset(dp, -1, sizeof dp);
    return dfs(cnt, 0, 1);
}

int main(){
    int l, r;
    while(cin >> l >> r >> mod) cout << solve(r) - solve(l - 1) << endl;
    return 0;
}