First question (based on google interview question). Giving a collection of numbers and you will need to find a matching pair that are equal to the number that I'll give you.

InterviewWithSwift

import UIKit
/*
 Question - I'm giving you a collection of numbers and you will need to find a matching pair that are equal to the number that I'll give you.
 
 So for example the collection of number will be: [1,2,3,9] and the sum that I'm looking for is 8.
 
 An another example will be [1,2,4,4] and the sum is 8
 
 A- so, I'm trying to understand. You are looking for a pair of numbers that add up to 8
 
 S - Yes
 
 A- So in the first example there is no pair of number and in the second example it's 4,4.
 
 S- Correct
 
 A- How do I get this numbers? Can I assume that they are in memory? an array?
 
 S- Yes they are in memory like an array you can also assume that they are ordered.
 
 A- Oh, Interesting!  How about repeating elements?
 
 if I'm getting an array of [1,2,4] Can I repeat 4 twice?
 
 S- you can have the same element but not in the same index place.
 
 A- How about this numbers? Are they integers? or floating?
 
 S- you can assume they are all integer
 
 A- negatives?
 
 S- Yes, you can have negative.
 
 A- So, the first simple solution to compare every element in the array. have 2 for loops go over each element in the array. Start with the first and the second element. (brute force) It's not efficient but it's a way to solve it.
 
 S- That would works. It's certainly would be time consuming
 
 A- I'm trying to look if I have 1 in the first place I need to look for a 7 somewhere so I can use binary search.
 
 I can find the sum of two numbers if it bigger then 8 I'll move the higher index and if it's smaller I'll move the low index right. That Will be linear iteration and I end if I find a pair of if they cross. It's better then binary because because the binary will go over every element so it will be Nlog(n) and the linear is just once O(1) ?
 
 S- Can you show me how it's works in a working environment?
 
 A- Show
 
 S- so what coding language do you prefer? Swift :)
 */


//brute force
func isSum(arr:[Int], sum:Int)->Bool
{
    for i in 0 ..< arr.count
    {
        
        for j in 1 ..< arr.count
        {
            if(arr[i] + arr[j] == sum){
                return true
            }
        
        }
        

    }
    return false
}
isSum(arr: [2,3,4,4], sum: 8)

// Linear Search
func IsSumlinearSearch( a: [Int], key: Int) -> Bool {
    var low = 0
    var high = a.count-1
    
    while low < high {
        print(a[high])
        if (a[low] + a[high] == key )  {
            return true
        }
        if (a[low] + a[high] > key ){
            high -= 1
        }
        else {
            low += 1
        }
    }
    return false
}
IsSumlinearSearch(a: [1,1,4,5,6], key: 8)

// What if I'll ask you to return the pair of numbers if it's true?
func IsSumlinearSearchReturnNum( a: [Int], key: Int) -> [Int]? {
    var low = 0
    var high = a.count-1
    
    while low < high {
        print(a[high])
        if (a[low] + a[high] == key )  {
            return [a[low],a[high]]
        }
        if (a[low] + a[high] > key ){
            high -= 1
        }
        else {
            low += 1
        }
    }
    return nil
}
IsSumlinearSearchReturnNum(a: [1,4,4,5,6], key: 8)