题解 | 小红的整数配对

import java.io.*;
import java.util.*;

public class Main {
   public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        String[] str = br.readLine().split("\\s+");
        int n = Integer.parseInt(str[0]);
        int k = Integer.parseInt(str[1]);

        String[] numStr = br.readLine().split("\\s+");
        int[] a = new int[n];

        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(numStr[i]);
        }

        Arrays.sort(a);

        long maxScore = 0;
        int i = n - 1;// 从末尾开始遍历
        // 从后往前贪心配对
        while (i >= 1) {
            if (a[i] - a[i - 1] <= k) {
                maxScore += (long) a[i] * a[i - 1];
                i -= 2;// 配对成功，跳过这两个元素
            } else {
                i -= 1;// 无法配对，只跳过当前元素
            }
        }

        out.println(maxScore);

        out.flush();
        out.close();
        br.close();
    }
}