Checking for particular types of matrix in JavaScript

Problem

We are required to write a JavaScript function that takes in a 2-D array of literals, arr, as the first and the only argument.

Our function should check if every diagonal from top-left to bottom-right has the same element.

If it is so, we should return true, false otherwise.

For example, if the input to the function is

Input

const arr = [
   [6, 7, 8, 9],
   [2, 6, 7, 8],
   [1, 2, 6, 7],
];

Output

const output = true;

Output Explanation

In the above array, the diagonals are −

[1], [2,2], [6,6,6], [7,7,7], [8,8], [9]

In each diagonal all elements are the same, so the answer is True.

Example

Following is the code −

 Live Demo

const arr = [
   [6, 7, 8, 9],
   [2, 6, 7, 8],
   [1, 2, 6, 7],
];
const checkMatrix = (arr = []) => {
   const validate = (row, col) => {
      while (
         row < arr.length
         && col < arr[0].length
         && arr[row + 1]
         && arr[row + 1][col + 1] !== undefined
      ) {
         if (arr[row + 1][col + 1] !== arr[row][col]) {
            return false
         }
         row += 1
         col += 1
      }
      return true
   }
   for (let i = 0; i < arr[0].length; i++) {
      if (!validate(0, i)) {
         return false
      }
   }
   for (let i = 0; i < arr.length; i++) {
      if (!validate(i, 0)) {
         return false
      }
   }
   return true
}
console.log(checkMatrix(arr));

Output

true