我正在研究一个项目，我必须读取文件并将内容输入2D数组。然后我要对每一行，每一列，和矩阵的周长求和。到目前为止，除了外围，一切正常。我试图为顶部行，底部行和两个外部列的中间创建单独的for循环。
矩阵文件如下所示:
1 2 3 4
2 4 6 8
2 4 6 8
3 2 3 4
所以周长加起来应该是42。现在我可以成功地将第一行和最后一行相加，得到22。然而，当我把列加到总数上时，我得到32。
代码如下:
import java.util.*; // Scanner class
import java.io.*; // File class
public class Lab10
{
static public void main( String [ ] args ) throws Exception
{
if ( args.length != 1 )
{
System.out.println("Error -- usage is: java Lab10 matdataN.txt");
System.exit( 0 );
}
//Requirement #1: first int value: # of rows, second int value: # of cols
File newFile = new File(args[0]);
Scanner in = new Scanner(newFile);
int numRows = in.nextInt();
int numCols = in.nextInt();
//Requirement #2: declare two-d array of ints
int[][] matrix;
matrix = new int[numRows][numCols];
//Requirement #3 & 4: read file one line at a time (nested for loops
//and nextInt()) and print
for (int i = 0; i < numRows; i++)
{
for (int j = 0; j < numCols; j++)
{
matrix[i][j] = in.nextInt();
System.out.print(matrix[i][j]+ " ");
}
System.out.println();
}
//Requirement #5: traverse each row and sum the values and display the sums
int rowTotal = 0;
for (int i = 0; i < numRows; i++)
{
rowTotal = 0;
for (int j = 0; j < numCols; j++)
{
rowTotal += matrix[i][j];
}
System.out.println("Sum for row = " + rowTotal);
}
//Requirement #6: traverse each column and sum the values and display the sums
int colTotal = 0;
for (int i = 0; i < numRows; i++)
{
colTotal = 0;
for (int j = 0; j < numCols; j++)
{
colTotal += matrix[j][i];
}
System.out.println("Sum for col = " + colTotal);
}
//Requirement #7: traverse the perimeter and sum the values and display the sum
//sum bottom row matrix
int perTotal = 0;
for (int i = (numRows-1); i < numRows; i++)
{
perTotal = 0;
for (int j = 0; j < numCols; j++)
{
perTotal += matrix[i][j];
}
}
//sum + top row matrix
for (int i = 0; i < numRows - (numRows-1); i++)
{
for (int j = 0; j < numCols; j++)
{
perTotal += matrix[i][j];
}
System.out.println("Sum of perimeter = " + perTotal);
}
// sum + first col middle
for (int i = 1; i < (numRows-1); i++)
{
for (int j = 0; j < numCols - (numCols-1); j++)
{
perTotal += matrix[j][i];
}
System.out.println("Sum = " + perTotal);
}
// sum + last col middle
for (int i = 1; i < (numRows-1); i++)
{
for (int j = (numCols-1); j < numCols; j++)
{
perTotal += matrix[j][i];
}
System.out.println(perTotal);
}
}
我建议你这样做:
int perTotal = 0;
// top and bottom row
for (int c = 0; c < numCols; c++)
perTotal += matrix[0][c] + matrix[numRows-1][c];
// left and right column
for (int r = 1; r < numRows-1; r++)
perTotal += matrix[r][0] + matrix[r][numCols-1];
// output
System.out.println("Perimeter=" + perTotal);
方法如下:
public static int perimeter(int[][] array) {
int perimter = 0;
for (int i = 0; i < array[0].length; i++) {
perimter += array[0][i] + array[array.length - 1][i];
}
for (int r = 1; r < array.length - 1; r++) {
perimter += array[r][0] + array[r][array[0].length - 1];
}
return perimter;
}
下面是你对你提供的数组的测试:
public static void main(String[] args) {system . out。println(周长(新int[][]{{1、2、2、3},{2,4,4,2},{3、6、6、3},{4、8、8、4}}));}
输出:42
在0.4.0版本中有一个la4j (Java线性代数)库可以处理这个任务(目前可以在GitHub上获得:https://github.com/vkostyukov/la4j，将在今年夏天在Maven上获得)。下面是一个简单的例子:
Matrix a = new Basic2DMatrix(...); // creates a real matrix
// calculates the sum of '1' row
double d1 = a.foldRow(1, Matrices.asSumAccumulator(0));
// calculates the sum of '2'
double d2 = a.foldColumn(2, Matrices.asSumAccumulator(0));
// the helper class that fetches border elements of matrix
class PerimeterFetcher implements MatrixFunction {
private int rows;
private int columns;
public PerimeterFectcher(int rows, int columns) {
this.rows = rows;
this.columns = columns;
}
@Override
public double evaluate(int i, int j, double value) {
return i == 0 ? value : j == 0 ? value : (i + 1) == rows ? value
: (j + 1) == columns ? value : 0;
}
}
// calculates the perimeter of matrix
double p = a.fold(Matrices.asSumFunctionAccumulator(0,
new PerimeterFetcher(a.rows(), a.columns())));
UPD:下一个版本的la4j(0.4.5)支持矩阵和向量的sum()方法:
Matrix a = new Basic2DMatrix(...);
double s = a.sum(); // wrapper around a.fold(...);
//Requirement #7: traverse the perimeter and sum the values and display the sum
int perTotal = 0;
// First line
for (int j = 0; j < numCols; j++)
{
perTotal += matrix[0][j];
}
// If there is only one line, then it is done.
if (numRows > 1)
{
// Last line
for (int j = 0; j < numCols; j++)
{
perTotal += matrix[numRows-1][j];
}
// Other lines
for (int i = 1; i < numRows -1); i++)
{
perTotal += matrix[i][0] + matrix[i][numcols -1];
}
}
//Perimeter
System.out.println("Perimter="+perTotal);
就这样做:
for (int i = 0; i < ROWS; i++){
for (int j = 0; j < COLUMNS; j++){
sum = sum + myArray[i][j];
}
}
System.out.print(sum);
谢谢大家!这么简单的方法。供参考:我最后做了
int perTotal = 0;
for (int i = 0; i < numCols; i++)
{
perTotal += matrix[0][i] + matrix[numRows-1][i];
}
for (int j = 1; j < numRows-1; j++)
{
perTotal += matrix[j][0] + matrix[j][numCols-1];
}
System.out.println("Perimeter = " + perTotal);
尝试如下:
import java.util.Scanner;
public class TwoDarray {
public static void main(String[] args)
{
Scanner scn=new Scanner(System.in);
System.out.print("Enter the first Rows of Array :"); //Input first Rows and Columns
int row1 = scn.nextInt();
System.out.print("Enter the first columns of Array:");
int col1 = scn.nextInt();
System.out.print("Enter the second Rows of Array :"); //Input second rows and column
int row2 = scn.nextInt();
System.out.print("Enter the second columns of Array:");
int col2 = scn.nextInt();
int arr1[][] = new int[row1][col1]; // Input the elements in first row and column
System.out.println("Enter the elements in First row and column");
for(int i=0;i<row1;i++)
{
for(int j=0;j<col1;j++)
{
arr1[i][j]=scn.nextInt();
}
}
int arr2[][] = new int[row2][col2]; // Input the elements in second row and column
System.out.println("Enter the elements in second row and column");
for(int i=0;i<row2;i++)
{
for(int j=0;j<col2;j++)
{
arr2[i][j]=scn.nextInt();
}
}
System.out.println("Output of first row and column is "); //output of first row and column
for(int i=0;i<row1;i++)
{
for(int j=0;j<col1;j++)
{
System.out.print(arr1[i][j]+" ");
} System.out.println();
}
System.out.println("output of secound row and column"); //out put of second row and column
for(int i=0;i<row2;i++)
{
for(int j=0;j<col2;j++)
{
System.out.print(arr2[i][j]+" ");
} System.out.println();
}
//sum of first and second row and column
int sum[][] = new int[row1][col1];
for(int i=0;i<row1;i++)
{
for(int j=0;j<col1;j++)
{
sum[i][j]=arr1[i][j]+arr2[i][j];
}
}
System.out.println("sum of two matrix output"); //sum of two matrix output
for(int i=0;i<row1;i++)
{
for(int j=0;j<col1;j++)
{
System.out.print(sum[i][j]+" ");
} System.out.println();
}
}
}
您可以简单地使用:
static int sumMultiArray(int[][] array) {
int sum = 0;
for (int[] ints : array) {
for (int number : ints) {
sum += number;
}
}
return sum;
}
private static int sumElementInArray(int[][] arrayWithElement) {
int sum = 0;
for (int i = 0; i < arrayWithElement.length; i++) {
sum += IntStream.of(arrayWithElement[i]).sum();
}
return sum;
}