Diagonal Difference | Solution | JavaScript

diagonal-difference.js

/* 
  Diagonal Difference Solution.
  sample matrix = [[1,2,3], [4,5,6], [7,8,9]]
*/ 
function diagonalDifference(matrix) {
   // length of input matrix.
    const length = matrix.length;
    let diagonal1 = 0, diagonal2 = 0;
  
    // Looping through the array and summing the diagonals.
    for(let i = 0; i < length; i++){
      // Calculating the primary diagonal.
        diagonal1 += matrix[i][i];
      // Reversing the second dimension of array to calculate secondary diagonal.
        diagonal2 += matrix[length -1 - i][i]
    }
    // return absolute difference value.
    return Math.abs(diagonal1 - diagonal2);  

}

Here is the matrix

3
11 2 4
4 5 6
10 8 -12

I've implemented above matrix but I'm getting an error NAN. Can you please let me know what's the issue?
let matrix = [[3],[11,2,4],[4,5,6],[10,8,-12]]
console.log(diagonalDifference(matrix));

Your code isn't implementable for different types of matrix. I think you have to test this code on the different test cases like:

4
-1 1 -7 -8
-10 -8 -5 -2
0 9 7 -1
4 4 -2 1

9
6 6 7 -10 9 -3 8 9 -1
9 7 -10 6 4 1 6 1 1
-1 -2 4 -6 1 -4 -6 3 9
-8 7 6 -1 -6 -6 6 -7 2
-10 -4 9 1 -7 8 -5 3 -5
-8 -3 -4 2 -3 7 -5 1 -5
-2 -7 -4 8 3 -1 8 2 3
-3 4 6 -7 -7 -8 -3 9 -6
-2 0 5 4 4 4 -3 3 0

The matrix should be n x m, where n = m , if your matrix isnt balanced you need to balance rows in the given matrix.

Please check out the example on below codesandbox link:
https://codesandbox.io/s/diagonal-difference-with-balance-matrix-61725c?file=/src/index.js

Although I dont know that expected outputs of given matixs, have a play around it and let me know if its makes sense or not.

function diagonalDifference(arr) {
    const {a, b} = arr.reduce((acc, cur, i) => {
        acc.a += arr[i][i]
        acc.b += arr[arr.length - 1 - i][i]
        return acc
    }, {a: 0, b: 0})
    return Math.abs(a - b)
}

function diagonalDifference(arr) {
    let n = arr.length - 1
    // caluclate the difference in every row 
    // e.g. first row: first - last element, second row: secondElement - (secondLast element)
    arr = arr.map((el,i) => el[i]-el[n-i]).reduce((p,c)=>p+c)

    return Math.abs(arr)
}

Alternative solution, just use the same For loop, to loop through in ascending and descending order:

function diagonalDifference(arr) {
    // Write your code here
    let firstDiagonalTotal = 0 
    let secondDiagonalTotal = 0  
    
    // firstDiagonal = arr[0][0] + arr[1][1] + arr[2][2]
    // secondDiagonal = arr[0][2] + arr[1][1] + arr[2][0]
    for (let i = 0, k = arr[0].length - 1; i < arr[0].length; i++, k--) {
        firstDiagonalTotal += arr[i][i]
        secondDiagonalTotal += arr[i][k]
    }

    return Math.abs(firstDiagonalTotal - secondDiagonalTotal)
}

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