题解 | 小红的整数配对

#include <cmath>
#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

#define ll long long
int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(false);
    ll n, k, ans = 0;
    cin >> n >> k;
    vector<ll> nums(n);
    for (auto& a : nums) {
        cin >> a;
    }
    sort(nums.begin(), nums.end(), greater<>());
    int i = 0;
    while (nums.size() > i+1) {
        if ((nums[i] - nums[i + 1]) <= k) {
            ans += nums[i + 1] * nums[i];
            i += 2;
        }
        else i++;
    }
    cout << ans;
}