HackerRank Js-Week2 4. Diagonal Difference

    AllenLi
    HackerRank

    Given a square matrix, calculate the absolute difference between the sums of its diagonals.
    For example, the square matrix arr is shown below:
    The left-to-right diagonal = 1 + 5 + 9 = 15. The right to left diagonal = 3 + 5 + 9 = 17. Their absolute difference is |15 – 17| = 2.

    給予一個矩陣，計算對角線之總和的絕對差。
例如，一個方正的矩陣 arr 如下：
123
456
789

從左到右的對角線為 1 + 5 + 9 = 15。從右到左的對角線為 3 + 5 + 9 = 17。
他們的絕對差是 | 15 - 17| = 2。

    Example 1:

    123
456
989

return 2

    solution:
    先簡單列出「左到右的對角線」，接著列出「右到左的對角線」，
    在用絕對值處理兩者相減，最後回傳該值。
    ex. 運用遍歷回圈的過程中，同步將左上與左下值加入對應的對角線中。

    Code 1: BigO(n)

    'use strict';

const fs = require('fs');
process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

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

process.stdin.on('end', function() {
    inputString = inputString.split('\n');

    main();
});

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

/*
 * Complete the 'diagonalDifference' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts 2D_INTEGER_ARRAY arr as parameter.
 */

function diagonalDifference(arr) {
    // Write your code here
    
    let leftToRight = 0,
        rightToLeft = 0
        
    for (let i = 0; i < arr.length; i++) {
        leftToRight += arr[i][i]
        rightToLeft += arr[arr.length - 1 - i][i]
    }
    
    return Math.abs(leftToRight - rightToLeft);
}

function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

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

    let arr = Array(n);

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

    const result = diagonalDifference(arr);

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

    ws.end();
}

    FlowChart:
    Example 1

    arr = [ [ 11, 2, 4 ], [ 4, 5, 6 ], [ 10, 8, -12 ] ]
leftToRight = arr[0][0] + arr[1][1] + arr[2][2]
rightToLeft = arr[2][0] + arr[1][1] + arr[0][2]

leftToRight += arr[i][i]
rightToLeft += arr[arr.length - 1 - i][i]

leftTORight = 0
rightToLeft = 0

step.1 i = 0
leftToRight += arr[0][0] //0 + 11 = 11
rightToLeft += arr[3 - 1 - 0][0] = arr[2][0] //0 + 4 = 4

step.2 i = 1
leftToRight += arr[1][1] //11 + 5 = 16
rightToLeft += arr[3 - 1 - 1][1] //4 + 5 = 9

step.3 i = 2
leftToRight += arr[2][2] //16 + (-12) = 4
rightToLeft ++ arr[3 - 1 - 2][2] //9 + 10 = 19

return Math.abs(leftToRight - rightToLeft) //|4 - 19| = 15

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