JDB JDB - 5 months ago 32
Java Question

Adding the diagonal values in a 2d array

I have the following 2d array

int [][] array = {{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
{10, 11, 12, 13, 14, 15, 16, 17, 18, 19},
{20, 21, 22, 23, 24, 25, 26, 27, 28, 29},
{30, 31, 32, 33, 34, 35, 36, 37, 38, 39},
{40, 41, 42, 43, 44, 45, 46, 47, 48, 49},
{50, 51, 52, 53, 54, 55, 56, 57, 58, 59},
{60, 61, 62, 63, 64, 65, 66, 67, 68, 69},
{70, 71, 72, 73, 74, 75, 76, 77, 78, 79},
{80, 81, 82, 83, 84, 85, 86, 87, 88, 89},
{90, 91, 92, 93, 94, 95, 96, 97, 98, 99}};


I have this code to find the sum of all the values in the array. How can I modify it to add only the diagonal values starting at 0 (0+11+22+33 etc.)?

public static int arraySum(int[][] array)
{
int total = 0;

for (int row = 0; row < array.length; row++)
{
for (int col = 0; col < array[row].length; col++)
total += array[row][col];
}

return total;
}

Answer

Since the diagonals are at perfect square you only need one loop to add the diagonals.


Adding diagonal from orgin:

public static int arraySum(int[][] array){
    int total = 0;

    for (int row = 0; row < array.length; row++)
    {

        total += array[row][row];
    }

    return total;
}

Add both diagonals:

Adding diagonal from orgin: (note it adds the center twice..you can subtract one if needed)

public static int arraySum(int[][] array){
    int total = 0;

    for (int row = 0; row < array.length; row++)
    {
        total += array[row][row] + array[array.length - row-1][array.length - row-1];
    }

    return total;
}
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