# Subtraction of alternate nodes of linked list in swift

Swift program for Subtraction of alternate nodes of linked list. Here problem description and other solutions.

``````import Foundation
/*
Swift 4 program for
Subtraction of the alternate nodes of linked list
*/
// Linked list node
{
var data: Int;
var next: LinkNode? ;
init(_ data: Int)
{
self.data = data;
self.next = nil;
}
}
class SingleLL
{
var tail: LinkNode? ;
init()
{
self.tail = nil;
}
func insert(_ data: Int)
{
if (self.head == nil)
{
// Add first node
}
else
{
// Add node at the end position
self.tail!.next = node;
}
// New last node
self.tail = node;
}
// Display linked list element
func display()
{
if (self.head == nil)
{
return;
}
// iterating linked list elements
while (temp  != nil)
{
print(" ",temp!.data, terminator: " →");
// Visit to next node
temp = temp!.next;
}
print(" NULL");
}
// Find the subtraction of all alternate
// nodes in linked list
func alternateSubtraction()
{
// Define resultant variables
var result: Int = 0;
var counter: Int = 0;
// Start to first node of linked list
// iterating linked list elements
while (temp  != nil)
{
if (counter % 2 == 0)
{
// When get alternate node
if (result == 0)
{
result = temp!.data;
}
else
{
result = result - temp!.data;
}
}
// Node counter
counter += 1;
// Visit to next node
temp = temp!.next;
}
print(" Alternate nodes subtraction :",result);
}
static func main()
{
let sll: SingleLL = SingleLL();
// 4 → 7 → 2 → 9 → 1 → 3 → 4 → 3 → 6 → NULL
sll.insert(4);
sll.insert(7);
sll.insert(2);
sll.insert(9);
sll.insert(1);
sll.insert(3);
sll.insert(4);
sll.insert(3);
sll.insert(6);
// Display of linked list nodes
sll.display();
// Test
sll.alternateSubtraction();
}
}
SingleLL.main();``````

Output

``````  4 →  7 →  2 →  9 →  1 →  3 →  4 →  3 →  6 → NULL
Alternate nodes subtraction : -9``````

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