Print Matrix Diagonally OR Diagonal order of Matrix.

Print Matrix Diagonally. OR
Loop diagonally through two dimensional array. OR
Traverse an array diagonally. OR
Print elements of Matrix in Diagonal order.

Algorithm

1. rowCount diagonals
2. (colCount - 1) diagonals.

1. Iterate "r" from 0 till rowCount
2. For each row, initialize "row=r" and "col=0" iterate till (row >=0 && col<collength )
3. Print matrix[row][col]
4. Decrement row-- and Increment col++

1. Iterate "c" from 1 till colCount
2. For each row, initialize "row=rowCount" and "col=c" iterate till (row >=0 && col < collength)
3. Print matrix[row][col]
4. Decrement row-- and Increment col++

Java Program to Print Matrix Diagonally.

package javabypatel.matrix;

/*
 Input:
   {1,  2,  3,  4},
   {5,  6,  7,  8},
   {9,  10, 11, 12},
   {13, 14, 15, 16},
   {17, 18, 19, 20},
   
Output:
   1
   5   2
   9   6   3
   13  10  7  4 
   17  14  11 8
   18  15  12
   19  16
   20  
 */

public class PrintMatrixDiagonally {

 public static void main(String[] args) {
  new PrintMatrixDiagonally();
 }

 public PrintMatrixDiagonally() {
  int[][] matrix = {
   {1,  2,  3,  4},
   {5,  6,  7,  8},
   {9,  10, 11, 12},
   {13, 14, 15, 16},
   {17, 18, 19, 20}
  };
  
  printMatrixDiagonally(matrix);
 }

 private void printMatrixDiagonally(int[][] matrix){
  
  int rowCount = matrix.length;
  int columnCount = matrix[0].length;
 
  for (int r = 0; r < rowCount; r++) {
   for (int row = r, col = 0; row >= 0 && col < columnCount; row--, col++) {
    System.out.print(matrix[row][col] + " "); 
   }
   System.out.println();
  }
  
  for (int c = 1; c < columnCount; c++) {
   for (int row = rowCount-1, col = c; row >= 0 && col < columnCount; row--, col++) {
    System.out.print(matrix[row][col] + " "); 
   }
   System.out.println();
  }

 }
 
}

package javabypatel.matrix;

public class PrintMatrixDiagonally {

    public static void main(String[] args) {
        int[][] matrix = {
            {1,  2,  3,  4},
            {5,  6,  7,  8},
            {9,  10, 11, 12},
            {13, 14, 15, 16},
            {17, 18, 19, 20}
        };

        printMatrixDiagonally(matrix);
    }

    private static void printMatrixDiagonally(int[][] matrix) {

        for (int i = 0 ; i < matrix.length ; i++) {
            int row = i;
            int col = 0;

            while (row >= 0 && col < matrix[0].length) {
                System.out.print(matrix[row][col] + " ");
                col++;
                row--;
            }
            System.out.println();
        }

        for (int i = 1 ; i < matrix[0].length ; i++) {
            int row = matrix.length-1;
            int col = i;

            while (row >= 0 && col < matrix[0].length) {
                System.out.print(matrix[row][col] + " ");
                col++;
                row--;
            }
            System.out.println();
        }
    }

}

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