如何对矩阵中的一行求和 [英] How to sum a row in a matrix

问题描述

编写方法:

public int sumRow(int[][] matrix, int row)

将2D数组中称为矩阵的行 row 求和.

that sums row row in the 2D array called matrix.

给出:

public void run()
{
    System.out.println(sumRow(new int[][]{{70,93,68,78,83},{68,89,91,93,72},{98,68,69,79,88}}, 2));
    System.out.println(sumRow(new int[][]{{1,1,1}, {2,2,2}, {3,3,3}}, 0));
    System.out.println(sumRow(new int[][]{{2,4,6,8,10}, {1,2,3,4,5}, {10,20,30,40,50}}, 2));
}

到目前为止，我有:

public int sumRow(int[][] matrix, int row)
{
    int sum = 0;
    for(int i = 0; i < matrix.length; i++)
    {
        for(int j = 0; j < matrix.length; j++)
        {
            sum = sum + matrix[j][i];
        }   
    }
    return sum;
}

我得到的输出分别是714、18和78，而应该分别是402、3和150.我在做什么错了?

The outputs I get are 714, 18, and 78 when they should be 402, 3, and 150. What am I doing wrong?

推荐答案

当您被要求对2D数组中的特定行求和时，您正在尝试对2D数组中的所有元素求和.在这种情况下，只需要一个for循环就可以遍历单行，就像遍历单个数组一样.循环将从第一个元素 matrix [row] [0] 开始，直到最后一个元素 matrix [row] [matrix [row] .length-1] ，因为 matrix [row] .length 是该矩阵特定行中的列/元素数.因此， matrix [row] .length-1 将是 matrix [row] 中最后一个元素的索引.这就是它的样子，

You're currently trying to sum all of the elements in the 2D array when you were asked to sum a specific row within the 2D array. In this case, you only need one for loop to traverse a single row like you would traverse a single array. The loop would start at the first element, matrix[row][0] and run until the last element, matrix[row][matrix[row].length - 1] since matrix[row].length is the number of columns/elements in that specific row of the matrix. Therefore, matrix[row].length - 1 would be the index of the last element in matrix[row]. Here's what it should look like,

public int sumRow(int[][] matrix, int row)
{
    int sum = 0;
    for(int i = 0; i < matrix[row].length; i++)
    {
        sum += matrix[row][i];
    }
    return sum;
}

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