java - 数三元组 - 第一种方法

Question

我正在 HackerRank 上进行此练习:

You are given an array and you need to find number of triplets of indices (i, j, k) such that the elements at those indices are in geometric progression for a given common ratio r and i < j < k.

完整练习:https://www.hackerrank.com/challenges/count-triplets-1/problem 我的编译器有问题。 这是代码:

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

public class Solution {

    // Complete the countTriplets function below.
    static long countTriplets(List<Long> arr, long r) {
        int counter = 0;

        for (int i = 0; i < arr.length() - 2; i++) {
            for (int j = i + 1; j < arr.length() - 1; j++) {
                if (arr[j] - arr[i] == r) {
                    for (int k = j + 1; k < arr.length(); k++) {
                        if (arr[k] - arr[j] == r) {
                            System.out.println("(" + arr[i] + "," + arr[j] + "," + arr[k] + ")");
                            counter++;
                            break;
                        }

                    }
                }
            }

        }
        ;
        return counter;

    }

    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String[] nr = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

        int n = Integer.parseInt(nr[0]);

        long r = Long.parseLong(nr[1]);

        List<Long> arr = Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" ")).map(Long::parseLong)
                .collect(toList());

        long ans = countTriplets(arr, r);

        bufferedWriter.write(String.valueOf(ans));
        bufferedWriter.newLine();

        bufferedReader.close();
        bufferedWriter.close();
    }
}

我有这个错误:

Solution.java:19: error: cannot find symbol
for (int i = 0; i < arr.length() -2; i++){
                       ^
  symbol:   method length()
  location: variable arr of type List<Long>
Solution.java:20: error: cannot find symbol
    for(int j = i + 1; j < arr.length() -1; j++){
                              ^
  symbol:   method length()
  location: variable arr of type List<Long>
Solution.java:21: error: array required, but List<Long> found
          if(arr[j] - arr[i] == r){
                ^
Solution.java:21: error: array required, but List<Long> found
          if(arr[j] - arr[i] == r){
                         ^
Solution.java:22: error: cannot find symbol
            for(int k = j + 1; k < arr.length(); k++){
                                      ^
  symbol:   method length()
  location: variable arr of type List<Long>
Solution.java:23: error: array required, but List<Long> found
                if(arr[k] - arr[j] == r){
                      ^
Solution.java:23: error: array required, but List<Long> found
                if(arr[k] - arr[j] == r){
                               ^
Solution.java:24: error: array required, but List<Long> found
System.out.println("(" +arr[i] + "," +arr[j] + "," +arr[k] +")");
                           ^
Solution.java:24: error: array required, but List<Long> found
System.out.println("(" +arr[i] + "," +arr[j] + "," +arr[k] +")");
                                         ^
Solution.java:24: error: array required, but List<Long> found
System.out.println("(" +arr[i] + "," +arr[j] + "," +arr[k] +")");
                                                       ^
10 errors

(我刚开始编程，所以我不知道代码是否正确)

================================================== ===============================

更新:我没有错误，但每个测试用例返回 0。

public class Solution {

    // Complete the countTriplets function below.
    static long countTriplets(List<Long> arr, long r) {

        // Long[] a = arr.toArray();
        int counter = 0;

        for (int i = 0; i < arr.size() - 2; i++) {
            for (int j = i + 1; j < arr.size() - 1; j++) {
                if (arr.get(j) - arr.get(i) == r) {
                    for (int k = j + 1; k < arr.size(); k++) {
                        if (arr.get(k) - arr.get(j) == r) {
                            System.out.println("(" + arr.get(i) + "," + arr.get(j) + "," + arr.get(k) + ")");
                            counter++;
                            break;
                        }

                    }
                }
            }
        }
        return counter;
    }
}

Answer 1

变量 arr 的输入类型是列表，而不是整数数组。 List是Collection的一个接口(interface)。

int[] arr = new int[];//是声明和数组的方式，任何元素都可以使用 arr[index] 访问

列表可以包含重复项，并且元素是有序的。 示例实现是 LinkedList(基于链接列表)和 ArrayList(基于动态数组)。

arr.size() 是获取集合大小的函数。此外，为了访问列表中的任何元素，使用了 arr.get(index) 函数。