用Java中的多维数ArrayList实现ArrayList的反向子集

Question

我正在尝试使用多维列表中提供的索引来反向列表中的子列表。我没有太多使用多维列表/数组的经验。我不明白为什么这行不通。

/*
   Given a List<Integer> list and List<List<Integer>> operations
   reverse the sublist and print out the list after all the operations have been done.
   Ex: [5, 3, 2, 1, 3]
       [[0,1], [1, 3]]
*/

import java.util.*;
public class ReverseParameters {
   public static void main(String[] args) {
       List<Integer> list = Arrays.asList(5, 3, 2, 1, 3);
       List<List<Integer>> operations = new ArrayList<>(2);
       for(int i= 0; i < 3; i++){
           operations.add(new ArrayList<>());
       }
       operations.get(0).add(1);
       operations.get(1).add(3);

       subList(list, operations);
   }
   public static void subList (List<Integer> list, List<List<Integer>> operations) {
       System.out.println(list);
       int vertCount = operations.size();
       for (int i = 0; i < vertCount; i++) {
           int edgeCount = operations.get(i).size();
           for (int j = 0; j < edgeCount; j++) {
               int startInd = i;
               int endInd = operations.get(i).get(j);
               int shift = endInd - startInd;
               int right = Math.min(i + shift - 1, list.size() - 1);
               int temp = 0;
               while (startInd < right) {
                   temp = list.get(startInd);
                   list.set(startInd, list.get(right));
                   list.set(right, temp);
                   startInd+=1;
                   right-=1;
               }
               System.out.println();
               System.out.printf(" %d %d%n", startInd, endInd);
               System.out.println();
           }
       }
       System.out.println(list);
   }
}

[5, 2, 3, 1, 3]

[3, 1, 2, 5, 3]

Answer 1

您使用不必要的变量使代码过于复杂，从而很难发现问题。请使用一个更简单的代码进行解释：

public static void main(String[] args) {
    List<Integer> list = Arrays.asList(5, 3, 2, 1, 3);
    List<List<Integer>> operations = new ArrayList<>(2);
    // Initialize your operations
    operations.add(Arrays.asList(0,1));
    operations.add(Arrays.asList(1,3));
    subList(list, operations);
}
public static void subList (List<Integer> list, List<List<Integer>> operations) {
    // You just iterate over the operations
    for (List<Integer> operation : operations) {
        // For each operation, store left and right indexes.
        int left = operation.get(0);
        int right = operation.get(1);
        // Iterate until both indexes find each other
        while (left < right) {
            // Swap left and right elements in input list
            int aux = list.get(left);
            list.set(left, list.get(right));
            list.set(right, aux);

            // Now you move your indexes
            ++left;
            --right;
        }
    }
    System.out.println(list);
}

请注意，根据问题的要求，您可能还需要验证操作索引是否在列表边界内，以便最终不会得到ArrayIndexOutOfBoundsException。所以对边缘情况一定要小心。