Added CF1874D

contest/cf1874/D.cpp

@@ -0,0 +1,54 @@
+#include <bits/stdc++.h>
+
+using ll = long long int;
+using ld = long double;
+
+const int MAXN = 3e3 + 19;
+const ld INF = 1e50L;
+
+int n, m;
+int q[MAXN], h, t;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::cin >> n >> m;
+
+    std::vector<ld> f(m + 1, INF), g(m + 1);
+
+    std::function<void(int, int, int, int)> solve = [&](int L, int R, int l, int r) {
+        if (l > r) return;
+        if (L == R) {
+            for (int i = l; i <= r; ++i) {
+                g[i] = f[L] + (ld)i / (i - L);
+            }
+            return;
+        }
+        int mid = (l + r) / 2;
+
+        int x = L;
+        ld t = f[x] + (ld)mid / (mid - x);
+        for (int i = L + 1; i < mid; ++i) {
+            ld n_t = f[i] + (ld)mid / (mid - i);
+            if (n_t < t) {
+                x = i;
+                t = n_t;
+            }
+        }
+        g[mid] = t;
+        solve(L, x, l, mid - 1);
+        solve(x, R, mid + 1, r);
+    };
+    f[0] = 0;
+    for (int i = 1; i <= n; ++i) {
+        g[0] = INF;
+        solve(0, m - 1, 1, m);
+        f.swap(g);
+    }
+
+    std::cout << std::fixed << std::setprecision(12);
+    std::cout << f[m] * 2 - n << '\n';
+
+    return 0;
+}