起床晚了10:20才发现有笔试第一题15分钟ak第二题做了一个半小时,一开始的做法时间复杂度爆了,只过24%,改进的代码如下,样例能够全过,自己也测试了别的数据,为什么实际用例送我大0蛋啊真的红温了package pdd_2;import java.util.*;// 注意类名必须为 Main, 不要有任何 package xxx 信息public class Main_1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); int group = in.nextInt(); int[] res = new int[group]; for (int i = 0; i < group; i++) { int count = in.nextInt(); int[] nums = new int[count]; double avg = 0; for (int j = 0; j < count; j++) { nums[j] = in.nextInt(); avg = avg + (double) nums[j]; } avg = avg / count; Arrays.sort(nums); Set<Set<Integer>> list = new HashSet<>(); Set<Set<Integer>> have = new HashSet<>(); getRes(nums, 0, nums.length - 1, avg, list, have); res[i] = list.size(); } for (int i = 0; i < res.length; i++) { System.out.println(res[i]); } } public static void getRes(int[] nums, int indexStart, int indexEnd, double avg, Set<Set<Integer>> list, Set<Set<Integer>> have) { if (indexStart == nums.length || indexEnd == -1 || indexStart >= indexEnd) { return; } Set<Integer> set = new HashSet<>(); set.add(indexStart); set.add(indexEnd); if (have.contains(set)) { return; } have.add(set); if (nums[indexStart] + nums[indexEnd] == avg * 2) { list.add(set); int x = 1; while (indexStart + x < indexEnd &amp;&amp; nums[indexStart + x] == nums[indexStart]) { x++; } int y = 1; while (indexStart < indexEnd - y &amp;&amp; nums[indexEnd - y] == nums[indexEnd]) { y++; } for (int i = 1; i <= x; i++) { for (int j = 1; j <= y; j++) { Set<Integer> s = new HashSet<>(); s.add(indexStart + i); s.add(indexEnd - j); if (s.size() == 2) { list.add(s); } } } getRes(nums, indexStart + x, indexEnd - y, avg, list, have); } if (nums[indexStart] + nums[indexEnd] > avg * 2) { getRes(nums, indexStart, indexEnd - 1, avg, list, have); } else { getRes(nums, indexStart + 1, indexEnd, avg, list, have); } }}