Diagonal Traversal of Matrix in Javascript

Diagonal Traversal of Matrix/2D Array in Javascript

Problem statement: 

In this post, we will traverse a given matrix/2D array diagonally (from center to top right corner). Refer below attached diagram for better understanding.

Diagonal pattern:

Expected Output:

expected output :

    1

    6

    11

    16

    2

    7

    12

    3

    8

    4

Input Matrix: 

let input2DArray = [

  [1, 2, 3, 4],

  [5, 6, 7, 8],

  [9, 10, 11, 12],

  [13, 14, 15, 16],

];

Solution Approach :

 When we think about the pattern required, we can confirm that there will always be n number of diagonals that we will be traversing, that means the outer loop will be from 0 to n-1. 

I have added below diagram for a matrix n x n:

Inner loop will be having 2 variables i and j as row and col of matrix. we can see that row index=i in each iteration starts from zero and j will start from the index= diagonal.

Let's write the code now:

let n = input2DArray.length;

for (let diag = 0; diag < n; diag++) {

// this loop will go from 0 to n-1, 

// that is for each diagonal as shown in diagram.

  for (let i = 0, j = diag; j < n && i < n; j++, i++) {

    // i is always starting with 0 

    // but j will start with index equals to diag.

    console.log(input2DArray[i][j]);

  }

}

Output:

1 6 11 16 2 7 12 3 8 4