518D - Ilya and Escalator

https://codeforces.com/contest/518/submission/173706602

Codeforces/518/D/D.cpp

@@ -0,0 +1,37 @@
+#include <iostream>
+#include <iomanip>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2005;
+
+int n, t;
+double p, f[N][N], ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> p >> t;
+
+    f[0][0] = 1;
+    for (int i = 1; i <= t; i++) {
+        f[i][0] = (1.0 - p) * f[i - 1][0];
+
+        for (int j = 1; j < n; j++) {
+            f[i][j] = p * f[i - 1][j - 1] + (1.0 - p) * f[i - 1][j];
+        }
+
+        f[i][n] = f[i - 1][n] + p * f[i - 1][n - 1];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        ans += f[t][i] * i;
+    }
+
+    cout << std::fixed << std::setprecision(6) << ans << endl;
+
+    return 0;
+}