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- #include <algorithm>
- #include <chrono>
- #include <iostream>
- #include <random>
- #include <vector>
- using namespace std;
- const int N = 3000000;
- double average_distance(const vector<int> &permutation) {
- double distance_sum = 0;
- for (int i = 0; i < N; i++)
- distance_sum += abs(permutation[i] - i);
- return distance_sum / N;
- }
- int main() {
- mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
- vector<int> permutation(N);
- for (int i = 0; i < N; i++)
- permutation[i] = i;
- shuffle(permutation.begin(), permutation.end(), rng);
- cout << average_distance(permutation) << '\n';
- for (int i = 0; i < N; i++)
- permutation[i] = i;
- for (int i = 1; i < N; i++)
- swap(permutation[i], permutation[uniform_int_distribution<int>(0, i)(rng)]);
- cout << average_distance(permutation) << '\n';
- }
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