1#include <vector>2#include <algorithm>3#include <iostream>4 5using namespace std;6 7bool f0(vector<int> &a, int m, int k) {8    int s = 0;9    for (int i = 0, j = 0; i < a.size(); i++) {10        while (a[i] - a[j] > m) j++;11        s += i - j;12    }13    return s >= k;14}15 16int f(vector<int> &a, int k) {17    sort(a.begin(), a.end());18 19    int g = 0;20    int h = a.back() - a[0];21    while (g < h) {22        int m = g + (h - g) / 2;23        if (f0(a, m, k)) {24            h = m;25        }26        else {27            g = m + 1;28        }29    }30 31    return g;32}33 34int main() {35    int n, k;36    cin >> n >> k;37    vector<int> a(n, 0);38    for (int i = 0; i < n; i++) {39        cin >> a[i];40    }41    cout << f(a, k) << endl;42    return 0;43}

假设输入总是合法的且 $1 \le a_i \le 10^8, n \le 10000, 1 \le k \le \dfrac {n(n-1)} 2$，完成下面的判断题和单选题: