Check if Linked List is null and just create a Node.
Otherwise, run to the end of the linked list and insert a node at the end.

/*
  Insert Node at the end of a linked list 
  head pointer input could be NULL as well for empty list
  Node is defined as 
  struct Node
  {
     int data;
     struct Node *next;
  }
*/
Node* Insert(Node *head,int data)
{
    if (!head){
        Node *node = new Node();
        node->data = data;
        return node;
    } 
    
    Node *temp = head;  
    while (true) {
        if (!temp->next){
            Node *node = new Node();
            node->data = data;
            temp->next = node;
            return head;
        } 
        temp = temp->next;
    }
}

https://www.hackerrank.com/challenges/2d-array

Had to refresh memory how to parse input from Hackerrank in Swift 3.

import Foundation;

func run() {
    var arr : [[Int]] = []
    for _ in 0 ... 5 { 
       let numbers = readLine()!.components(separatedBy: [" "]).map { Int($0)! }
       arr.append(numbers);
    }
    
    var maxSum = calculateHourglass(arr: arr, x: 0, y: 0)
    
    for i in 0 ... 3 {
        for j in 0 ... 3 {
             let result = calculateHourglass(arr: arr, x: i, y: j)
             if (maxSum < result){
                maxSum = result
             }
        }
    }
    
    print(maxSum)
}

func calculateHourglass(arr: [[Int]], x: Int, y: Int) -> Int {
   var sum = 0
   for i in x ... x+2 {
       if (i == x+1) {
        sum += arr[i][y+1]
       } else {
        for j in y ... y+2 {
            sum += arr[i][j]
        }
       }
   } 
   return sum
}

run()

Problem

Given a square matrix of size , calculate the absolute difference between the sums of its diagonals.

Input Format

The first line contains a single integer, . The next lines denote the matrix’s rows, with each line containing space-separated integers describing the columns.

Output Format

Print the absolute difference between the two sums of the matrix’s diagonals as a single integer.

Sample Input

3
11 2 4
4 5 6
10 8 -12
Sample Output

15
Explanation

The primary diagonal is:
11
5
-12

Sum across the primary diagonal: 11 + 5 – 12 = 4

The secondary diagonal is:
4
5
10
Sum across the secondary diagonal: 4 + 5 + 10 = 19
Difference: |4 – 19| = 15

Solution

// read the integer n
var n = Int(readLine()!)!
// declare 2d array
var arr : [[Int]] = []

// read array row-by-row
for index in 0..<n {
    arr.append(readLine()!.characters.split(" ").map{Int(String($0))!})
}
var preimaryDiagonalSum = 0
var secondaryDiagonalSum = 0
for index in 0..<n {
    preimaryDiagonalSum = preimaryDiagonalSum + arr[index][index]
    secondaryDiagonalSum = secondaryDiagonalSum + arr[index][n-index-1]
}

print(abs(preimaryDiagonalSum - secondaryDiagonalSum))