创建多维数组列表

Question

为什么这样做:

List<ArrayList<Integer>> input = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> row1 = new ArrayList<Integer>();
ArrayList<Integer> row2 = new ArrayList<Integer>();
input.add(row1);
input.get(0).add(2);
input.get(0).add(3);
input.get(0).add(4);
input.add(row2);
input.get(1).add(5);
input.get(1).add(6);
input.get(1).add(7);

ArrayList<Integer> row1 = new ArrayList<Integer>();
row1.add(2);
row1.add(3);
row1.add(4);
row1.add(5);
ArrayList<Integer> row2 = new ArrayList<Integer>();
row1.add(6);
row1.add(7);
row1.add(8);
row1.add(9);
input.add(row1);
input.add(row2);

第一个创建一个2X3矩阵，第二个创建一个2D数组，其第一个元素包含'row1'和'row2'中的所有数字。

TIA !

Answer 1

您没有在row2中添加任何内容。

改变

ArrayList<Integer> row2 = new ArrayList<Integer>();
row1.add(6);
row1.add(7);
row1.add(8);
row1.add(9);

ArrayList<Integer> row2 = new ArrayList<Integer>();
row2.add(6);
row2.add(7);
row2.add(8);
row2.add(9);

Answer 2

您将所有元素添加到row1中，因此输出与预期一致。

。您正在使用

row1.add(6);

不是

row2.add(6)

Answer 3

矩阵2D &实施:3 d

import java.util.ArrayList;
import java.util.List;
public class Matrix {
    private int rows;
    private int cols;
    private int depth;
    private List<Integer> list;
    public Matrix(int rows, int cols, List<Integer> list) {
        this.rows = rows;
        this.cols = cols;
        this.list = list;
    }
    public Matrix(int rows, int cols, int depth, List<Integer> list) {
        this.rows = rows;
        this.cols = cols;
        this.depth = depth;
        this.list = list;
    }
    public Integer get2D(int row, int col) {
        Integer elem = null;
        if (row < rows && col < cols) {
            int index = row * cols + col;
            elem = list.get(index);
        }
        return elem;
    }
    public boolean set2D(int row, int col, Integer val) {
        boolean flag = false;
        if (row < rows && col < cols) {
            int index = row * cols + col;
            list.set(index, val);
            flag = true;
        }
        return flag;
    }
    public Integer get3D(int row, int col, int dep) {
        Integer elem = null;
        if (row < rows && col < cols && dep <depth) {
            int index = dep * rows * cols + row * cols + col;
            elem = list.get(index);
        }
        return elem;
    }
    public boolean set3D(int row, int col, int dep, Integer val) {
        boolean flag = false;
        if (row < rows && col < cols && dep <depth) {
            int index = dep * rows * cols + row * cols + col;
            list.set(index, val);
            flag = true;
        }
        return flag;
    }
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            list.add(i);
        }
        Matrix mat2d = new Matrix(2, 3, list);
        System.out.println(mat2d.get2D(1, 2));
        Matrix mat3d = new Matrix(2, 2, 5, list);
        System.out.println(mat3d.get3D(1, 1, 3));
    }
}

数组二维实现:

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
public class Array2D {
    private int rowNum;
    private Map<Integer, List<Integer>> rows;
    public Array2D(int rowNum) {
        this.rowNum = rowNum;
        rows = new TreeMap<Integer, List<Integer>>();
        for (int i = 0; i < rowNum; i++) {
            rows.put(i, new ArrayList<Integer>());
        }
    }
    public Integer get(int row, int col) {
        Integer elem = null;
        if (row < rowNum) {
            List<Integer> list = rows.get(row);
            if (col < list.size())
                elem = list.get(col);
        }
        return elem;
    }
    public boolean set(int row, int col, Integer val) {
        boolean flag = false;
        if (row < rowNum) {
            List<Integer> list = rows.get(row);
            if (col < list.size())
                list.set(col, val);
        }
        return flag;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
    }
}