Question

我的问题是，如何将两个ArrayList相加？我要做的是导入两个单独的文件（包含2d数组）并将它们放入单独的arraylists中。从那里我试图将这两个数组列表相乘，然后让我的输出文件是输入的2d数组的乘积的二维数组。简而言之，我有两个输入文件（每个文件是一个单独的二维数组），我必须把这两个输入文件，并将它们相乘。我的输出文件应该是一个单独的2d数组。

到目前为止，我的代码如下：

package Matrix;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Scanner;

public class Matrix {

public static void multiply(File input_file1, File input_file2, File output_file) {



    try {
        Scanner scanner = new Scanner(input_file1);
        PrintWriter printer = new PrintWriter(output_file);
        ArrayList<Integer> file1 = new ArrayList<Integer>();
        while (scanner.hasNextInt()){
            file1.add(scanner.nextInt());
        }
        scanner.close();
        printer.close();

    }catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    try {
        Scanner scanner = new Scanner(input_file1);
        PrintWriter printer = new PrintWriter(output_file);
        ArrayList<Integer> file2 = new ArrayList<Integer>();
        while (scanner.hasNextInt()){
            file2.add(scanner.nextInt());
        }
        scanner.close();
        printer.close();
    }catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

}

Answer 1

//method that returns a double 2d matrix and takes two 2d matrices as parameters
public static double[][] multiply(double[][] A, double[][] B) {
        //make sure the matrices are the same size
        int mA = A.length;
        int nA = A[0].length;
        int mB = B.length;
        int nB = B[0].length;
        if (nA != mB) throw new RuntimeException("Matices are not the same");
        //create a new matrix to hold answer
        double[][] C = new double[mA][nB];

        //loop and multiply
        for (int i = 0; i < mA; i++)
            for (int j = 0; j < nB; j++)
                for (int k = 0; k < nA; k++)
                    C[i][j] += A[i][k] * B[k][j];
        return C;
    }

从ArrayList转换为Array

的帮助方法

ArrayList<ArrayList<String>> mainList = new ArrayList<ArrayList<String>>();
// populate this list here
//more code

// convert to an array of ArrayLists
ArrayList<String[]> tempList = new ArrayList<String[]>();
for (ArrayList<String> stringList : mainList){
    tempList.add((String[])stringList.toArray());
}

//Convert to array of arrays - 2D array
String [][]list = (String[][])tempList.toArray();

算法的步骤基本上是：

打开文件
读入arrayList
使用辅助方法转换为2d数组
在其他文件上重复1-3
将两个2d数组传递给乘法方法
做一个快乐的舞蹈

如何将2个ArrayLists相乘？

1 个答案: