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CSES Problem Set/Counting Numbers.cpp

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+/* Problem URL: https://cses.fi/problemset/task/2220 */
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+vvvvl memo;
+
+void dec(int i, string &a)
+{
+    if (a[i] == '0') {
+        a[i] = '9';
+        dec(i - 1, a);
+        return;
+    }
+
+    a[i] -= 1;
+}
+
+ll dp(int i, int prev, int started, int under, string &a)
+{
+    if (i >= memo.size()) {
+        return 1;
+    }
+
+    ll &ans = memo[i][prev][started][under];
+    if (ans != -1) {
+        return ans;
+    }
+
+    ans = 0;
+
+    for (char j = under ? 9 : a[i] - '0'; j >= 0; j--) {
+        if (j != prev || !started) {
+            ans += dp(i + 1, j, j != 0 || started, j < a[i] - '0' || under, a);
+        }
+    }
+
+    return ans;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    ll ai, bi;
+    cin >> ai >> bi;
+    string a = to_string(ai);
+    string b = to_string(bi);
+
+    memo.assign(b.size(), vvvl(10, vvl(2, vl(2, -1))));
+    ll ans = dp(0, 0, 0, 0, b);
+    if (a != "0") {
+        dec(a.size() - 1, a);
+        memo.assign(a.size(), vvvl(10, vvl(2, vl(2, -1))));
+        ans -= dp(0, 0, 0, 0, a);
+    }
+
+    cout << ans << '\n';
+}