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Luogu/P2503/P2503.cpp
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45
Luogu/P2503/P2503.cpp
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#include <iostream>
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#include <algorithm>
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#include <cmath>
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#include <iomanip>
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#include <numeric>
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#include <random>
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#include <vector>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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int n, m;
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double ans = 1e9;
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std::mt19937 rng(std::random_device{}());
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cin >> n >> m;
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std::vector<int> a(n);
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for (int& x : a) cin >> x;
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for (int i = 0; i < 1000000; i++) {
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std::vector<int> b(m);
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std::shuffle(a.begin(), a.end(), rng);
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for (int x : a) {
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*std::min_element(b.begin(), b.end()) += x;
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}
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double avg = static_cast<double>(std::accumulate(b.begin(), b.end(), 0)) / m;
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double variance = std::sqrt(std::accumulate(b.begin(), b.end(), 0.0, [&](double sum, int x) { return sum + std::pow(avg - x, 2); }) / m);
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ans = std::min(ans, variance);
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}
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cout << std::fixed << std::setprecision(2) << ans << endl;
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return 0;
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}
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