how_to_use_assert_module.js

'use strict';

const fs = require('fs');
const assert = require('assert').strict;

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', function() {
    inputString = inputString.replace(/\s*$/, '')
        .split('\n')
        .map(str => str.replace(/\s*$/, ''));

    main();
});

function readLine() {
    return inputString[currentLine++];
}

// Complete the diagonalDifference function below.
function diagonalDifference(arr) {
    const get = (plus, col = plus ? 0 : arr.length - 1, row = 0, res = 0) => {
        if (row === arr.length) {
            return res
        }
        return get(
            plus,
            plus ? col + 1 : col - 1,
            row + 1,
            res + arr[row][col],
        )
    }

    return Math.abs(get(true) - get(false))
}

function unittest() {
    let input = [[ 11, 2, 4 ], [ 4, 5, 6 ], [ 10, 8, -12 ]]
    let expected = 15
    assert.strictEqual(15, diagonalDifference(input))
}

unittest()

function main() {
    const ws = fs.createWriteStream('/dev/stdout');

    const n = parseInt(readLine(), 10);

    let arr = Array(n);

    for (let i = 0; i < n; i++) {
        arr[i] = readLine().split(' ').map(arrTemp => parseInt(arrTemp, 10));
    }

    const result = diagonalDifference(arr);

    ws.write(result + '\n');

    ws.end();
}