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kattis/25-2-2025/unicycle-counting.cc

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+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+void solve() {
+  string line;
+
+  while (getline(cin, line)) {
+    istringstream iss(line);
+    ll m, n;
+    iss >> m >> n;
+    ll x;
+    vector<ll> tires;
+    vector<bool> has(m + 1, false);
+
+    while (n--) {
+      iss >> x;
+      tires.push_back(x);
+      has[x] = true;
+    }
+
+    ll ans = 0;
+    ll i = 0;
+
+    while (i < tires.size()) {
+      while (i < tires.size() && !has[tires[i]]) {
+        i++;
+      }
+
+      if (i >= tires.size()) {
+        break;
+      }
+
+      if (i == tires.size() - 1) {
+        ++ans;
+        break;
+      }
+
+      ll best_count = 0;
+      ll best_delta = 0;
+
+      for (int advance = i + 1; advance < tires.size(); ++advance) {
+        ll count = 0;
+        ll delta = tires[advance] - tires[i];
+        ll cur = tires[i];
+        bool bad = false;
+
+        while (cur <= m - 1) {
+          if (has[cur]) {
+            ++count;
+          } else {
+            bad = true;
+            break;
+          }
+          cur += delta;
+        }
+
+        if (bad) {
+          continue;
+        }
+
+        if (count > best_count) {
+          best_count = count;
+          best_delta = delta;
+        }
+      }
+
+      if (best_delta == 0) {
+        has[tires[i]] = false;
+        ++ans;
+        continue;
+      }
+
+      ll cur = tires[i];
+      while (cur <= m - 1) {
+        has[cur] = false;
+        cur += best_delta;
+      }
+
+      ++ans;
+    }
+
+    cout << ans << endl;
+  }
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+
+  int t = 1;
+  // cin >> t;
+
+  while (t--) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}