Question

我正在编写一个尽可能高效地乘法矩阵（2d数组）的程序，为此我需要将我的两个数组分成两个，然后将它们发送到第二个程序进行乘法运算。我遇到的问题是如何在特定点（中途）将2d阵列分成两个2d阵列。有没有人有任何想法？

Answer 1

假设你有一个像这样的二维数组


String[][] array= new String[][]
{
    {"a","b","c"},
    {"d","e","f"},
    {"h","i","j"},
    {"k","l","m"}
};

现在你需要一种方法来在中间点分割这些数组。让我们得到中途点。弄清楚阵列有多大，然后把它切成两半。请注意，如果数组不是偶数长度，您还必须处理。示例，长度为3.如果是这种情况，我们将使用Math.floor()函数。


int arrayLength = array.length;
int halfWayPoint = Math.floor(arrayLength/2);
//we also need to know howmany elements are in the array
int numberOfElementsInArray = array[0].length;

现在我们拥有了从一个创建两个2d数组所需的所有信息。现在我们必须明确地复制创建和复制数据。


//the length of the first array will be the half way point which we already have
String [][] newArrayA = new String[halfWayPoint][numberOfElementsInArray];
//this copies the data over
for(int i = 0; i < halfWayPoint; i++)
{
    newArrayA[i] = array[i];
}

//now create the other array
int newArrayBLength = array.length - halfWayPoint;
String[][] newArrayB = new String[newArrayBLength][numberOfElementsInArray];
/*
 * This copies the data over. Notice that the for loop starts a halfWayPoint.
 * This is because this is where we left of copying in the first array.
 */
for(int i = halfWayPoint; i < array.length; i++)
{
    newArrayB[i] = array[i];
}

你做完了！

现在，如果你想做得更好一点，你可以这样做


int half = Math.floor(array/2);
int numberOfElementsInArray = array[0].length;
String [][] A = new String[half][numberOfElementsInArray];
String [][] B = new String[array.length - half][numberOfElementsInArray];
for(int i = 0; i < array.length; i++)
{
    if(i < half)
    {
        A[i] = array[i];
    }
    else
    {
        B[i] = array[i];
    }

}

最后，如果你不想明确地这样做，你可以使用内置函数。 System.arraycopy()就是一个例子。以下是其api System.arraycopy()

的链接


int half = Math.floor(array/2);
int numberOfElementsInArray = array[0].length;
String [][] A = new String[half][numberOfElementsInArray];
String [][] B = new String[array.length - half][numberOfElementsInArray];
System.arraycopy(array,0,A,0,half);
System.arraycopy(array,half,B,0,array.length - half);

java：如何将2d数组拆分为两个2d数组

1 个答案: