java - Java 中的锯齿状数组 : Converting char[][] and ArrayList>

Question

如何转换以下内容，使其本质上是 ArrayList 的锯齿状嵌套 ArrayList，每行/列都是字符列表？

   //Following excerpt from https://www.geeksforgeeks.org/jagged-array-in-java/
   int r = 5;
        //Need this to have capacity to hold list of chars (eg, each row/col index can be empty, //have 1 char, or multiple chars
        char toFill = new Variable(" ");

        // Declaring 2-D array with 5 rows... need it to be ArrayList<ArrayList<char>>
        char matrix[][] = new Variable[r][];


        // Creating a 2D array such that first row
        // has 1 element, second row has two
        // elements and so on.
        for (int i=0; i<matrix.length; i++) {
            matrix[i] = new char[i + 1];
        }

        // Initializing array
        int count = 0;
        for (int i=0; i<matrix.length; i++) {
            for (int j = 0; j < matrix[i].length; j++) {
                matrix[i][j] = toFill;
            }
        }        

Answer 1

实际上列表是动态结构，您不需要像数组等静态结构那样预先定义它们的大小。他是一个示例程序，直接将锯齿状数组转换为锯齿状列表列表。我尽力保留尽可能多的结构，以便您更容易理解。代码看起来仍然有点“数组式”(我实际上不喜欢它，因为它有点不自然)，但我希望你明白这个想法。

package de.scrum_master.stackoverflow.q60367936;

import java.util.ArrayList;
import java.util.List;

/**
 * Demonstrate 2-D jagged array/list such that first row has 1 element,
 * second row has two elements and so on.
 */
class Main {
  private static void jaggedArray() {
    int r = 5;

    // Declaring 2-D array with 5 rows
    int arr[][] = new int[r][];

    // Creating a 2D array such that first row has 1 element, second row has two elements and so on.
    for (int i = 0; i < arr.length; i++)
      arr[i] = new int[i + 1];

    // Initializing array
    int count = 0;
    for (int i = 0; i < arr.length; i++)
      for (int j = 0; j < arr[i].length; j++)
        arr[i][j] = count++;

    // Displaying the values of 2D Jagged array
    System.out.println("Contents of 2D Jagged Array");
    for (int i = 0; i < arr.length; i++) {
      for (int j = 0; j < arr[i].length; j++)
        System.out.print(arr[i][j] + " ");
      System.out.println();
    }
  }

  private static void jaggedArrayList() {
    int r = 5;

    // Declaring 2-D list of lists
    List<List<Integer>> arr = new ArrayList<>();

    // Adding empty sub list to main list
    for (int i = 0; i < r; i++)
      arr.add(new ArrayList<Integer>());

    // Initializing 2-D list
    int count = 0;
    for (int i = 0; i < r; i++)
      for (int j = 0; j <= i; j++)
        arr.get(i).add(count++);

    // Displaying the values of 2D Jagged list
    System.out.println("Contents of 2D Jagged ArrayList");
    for (List<Integer> list : arr) {
      for (Integer i : list)
        System.out.print(i + " ");
      System.out.println();
    }
  }

  public static void main(String[] args) {
    jaggedArray();
    System.out.println("\n------------------------------\n");
    jaggedArrayList();
  }
}

控制台日志:

Contents of 2D Jagged Array
0 
1 2 
3 4 5 
6 7 8 9 
10 11 12 13 14 

------------------------------

Contents of 2D Jagged ArrayList
0 
1 2 
3 4 5 
6 7 8 9 
10 11 12 13 14 

如您所见，数组和列表变体都会产生相同的结果。无论您使用List<List<Integer>>或List<List<Char>>对于算法来说并不重要。