P4127 [AHOI2009]同类分布

https://www.luogu.com.cn/record/86021113

Luogu/P4127/P4127.cpp

@@ -0,0 +1,55 @@
+#include <iostream>
+#include <bitset>
+#include <cstring>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+long long a, b, f[20][200][200], ans;
+int c[20], p;
+
+long long dfs(int len, int s, int x, bool limit) {
+    if (s + 9 * len < p) return 0;
+    if (!limit && f[len][s][x] != -1) return f[len][s][x];
+    if (!len) return s == p && x == 0;
+
+    int n = limit ? c[len] : 9;
+    long long res = 0;
+
+    for (int i = 0; i <= n && i + s <= p; i++)
+        res += dfs(len - 1, s + i, (x * 10 + i) % p, limit && (i == c[len]));
+
+    if (!limit) f[len][s][x] = res;
+
+    return res;
+}
+
+long long calc(long long x) {
+    int cnt = 0;
+
+    while (x) {
+        c[++cnt] = x % 10;
+        x /= 10;
+    }
+
+    long long res = 0;
+
+    for (p = 1; p <= cnt * 9; p++) {
+        memset(f, 0xff, sizeof(f));
+        res += dfs(cnt, 0, 0, 1);
+    }
+
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> a >> b;
+
+    cout << calc(b) - calc(a - 1) << endl;
+
+    return 0;
+}