题解 | 小红的整数配对

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        ArrayList<Long> list = new ArrayList<>();
        // 注意 hasNext 和 hasNextLine 的区别
        long n = in.nextLong();
        long k = in.nextLong();
        for (int i = 0; i < n; i++) {
            list.add(in.nextLong());
        }
        long count = 0;
        list.sort(Collections.reverseOrder());

        for (int i = 0; i < list.size() - 1;) {
            if (list.get(i) - list.get(i + 1) <= k) {
                count +=  list.get(i) * list.get(i + 1);
                i += 2;
            } else {
                i += 1;
            }
        }
        System.out.println(count);
    }
}