java:如何将2d数组拆分为两个2d数组

Question

我正在编写一个程序来尽可能有效地乘法矩阵(2d数组),为此我需要将我的两个数组分成两个,并将它们发送到第二个程序进行乘法.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字符串

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

现在,您需要一种方法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.例如,长度为3.如果是这种情况,我们将使用该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,如果您不想明确地执行此操作,则可以使用内置函数.System.arraycopy()就是一个例子.这是它的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);