您好 那个第三题是怎么做的 我没碰过这种题 第四道题我过了 给你看看 public class Main { public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); int[] nums = new int[n]; for(int i = 0; i < n; i++){ nums[i] = in.nextInt(); } Map<Integer, Integer> left = new HashMap<>(); Map<Integer, Integer> right = new HashMap<>(); left.put(nums[0],1); for(int i = 2; i < n; i++){ right.put(nums[i], right.getOrDefault(nums[i],0)+1); } long ans= 0; for(int mid = 1; mid < n-1; mid++){ for (Map.Entry<Integer,Integer> l: left.entrySet()){ ans += (long) l.getValue() * ( right.getOrDefault(nums[mid] * 3-l.getKey(),0)); } left.put(nums[mid],left.getOrDefault(nums[mid],0)+1); right.put(nums[mid+1],right.get(nums[mid+1])-1); } System.out.println(ans); } }