CODEWITHSUNDEEP
javaarraysmatrixdiagonal
Rpp
Rpp

Reputation: 113

How to iterate a 2d array diagonally from top left to bottom right

I am trying to iterate a square 2d array for all diagonals from top left to bottom right. I have code to iterate from bottom left to top right but I need to adapt it to also iterate the other way. 

public static void main(String[] args) {
       int[][] a = {
                {1,   2,  3,  4},
                {0,   1,  2,  3},
                {-1,  0,  1,  2},
                {-2, -1,  0,  1},
        };
        for (int j = 0; j <= a.length + a.length - 2; j++) {
            for (int k = 0; k <= j; k++) { // cols
                int l = j - k; //  rows
                if (l < a.length && k < a.length) {
                    System.out.print(a[l][k] + " ");
                }
            }
            System.out.println();
        }
}

The results are: 

1 
0 2 
-1 1 3 
-2 0 2 4 
-1 1 3 
0 2 
1

Which is the bottom left to top right diagonals. How can I adapt the method to print diagonals the other way to produce the following results:

-2
-1 -1
0 0 0
1 1 1 1
2 2 2 
3 3
4

Thanks for your help.

Upvotes: 3

Views: 2850

Answers (1)

Wisthler
Wisthler

Reputation: 587

Just have to mirror the row address

public static void main(String[] args) {
       int[][] a = {
                {1,   2,  3,  4},
                {0,   1,  2,  3},
                {-1,  0,  1,  2},
                {-2, -1,  0,  1},
        };
        for (int j = 0; j <= a.length + a.length - 2; j++) {
            for (int k = 0; k <= j; k++) { // cols
                int l = j - k; //  rows
                int mirror = a.lenght - l;
                if (mirror >= 0 && mirror < a.length && k < a.length) {
                    System.out.print(a[mirror][k] + " ");
                }
            }
            System.out.println();
        }
}

Upvotes: 4

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