#1816. 【2017.3 长乐省选集训 Day18 T2】子集

https://sjzezoj.com/submission/66531

S2OJ/1816/1816.cpp

@@ -0,0 +1,56 @@
+#include <iostream>
+#include <algorithm>
+#include <iomanip>
+#include <iterator>
+#include <numeric>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, a[N], s[N];
+double ans;
+
+double calc(int pos, int len) {
+    return static_cast<double>(s[n] - s[n - len] + s[pos] - s[pos - len - 1]) / (len * 2 + 1);
+}
+
+int solve(int x) {
+    int l = 1,
+        r = std::min(x - 1, n - x),
+        res = 0;
+
+    while (l <= r) {
+        int mid = (l + r) >> 1;
+
+        if (calc(x, mid - 1) <= calc(x, mid)) {
+            res = mid;
+            l = mid + 1;
+        } else {
+            r = mid - 1;
+        }
+    }
+
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    std::copy_n(std::istream_iterator<int>(cin), n, a + 1);
+    std::sort(a + 1, a + 1 + n);
+    std::partial_sum(a + 1, a + 1 + n, s + 1);
+
+    for (int i = 2; i < n; i++) {
+        ans = std::max(ans, calc(i, solve(i)) - a[i]);
+    }
+
+    cout << std::fixed << std::setprecision(5) << ans << endl;
+
+    return 0;
+}