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Let's Code : Remember we have to pass sorted array to this function : func numberOfSumPair(sortedArray : [ Int ] , key : Int ) -> Int {     var startPointer = 0     var endPointer = sortedArray. count - 1     var sumPairs = 0     if sortedArray. count < 2 {         return sumPairs     }     while startPointer < endPointer {         let sum = sortedArray[startPointer] + sortedArray[endPointer]         if sum == key {             print ( "Pairs : \ ( sortedArray[startPointer] ) + \ ( sortedArray[endPointer] )" )             sumPairs += 1             startPointer += 1         }         if sum > key {             endPointer -= 1 ...

Let's Code //: Playground - noun: a place where people can play import UIKit import Foundation var array : [ Int ] = [ 1 , 4 , 2 , 3 , 5 , 6 , 76 , 32 , 43 , 12 , 55 , 88 , 99 , 49 , 76 , 78 , 90 , 11 , 99 ] let key = 55 func binarySearch(array : [ Int ] , key : Int ) -> Bool {     let minIndex = 0     let maxIndex = array. count - 1     let midIndex = maxIndex / 2     let midValue = array[midIndex]          if (key < array[minIndex] || key > array[maxIndex]){         return false     }     if key < midValue {         let arraySlice = Array (array[ 0 ...midIndex - 1 ])         return binarySearch (array: arraySlice, key: key)     }     if key > midValue {         let arraySlice = Array (array[midIndex + 1 ...maxIndex]) ...

Complexity : O(n log n) Let's Code : //: A UIKit based Playground for presenting user interface    import UIKit import Foundation var sortThisArray : [ Int ] = [ 11 , 2 , 43 , 12 , 45 , 2 , 42 , 66 , 70 , 21 , 23 , 48 , 88 , 65 , 99 , 21 ] func merge(left:[ Int ],right:[ Int ]) -> [ Int ] {     var mergedArr : [ Int ] = []     var left = left     var right = right          while left. count > 0 && right. count > 0 {         if left. first ! < right. first ! {             mergedArr. append (left. removeFirst ())         }         else {             mergedArr. append (right. removeFirst ())         }     }     return mergedArr + left + right } func mergeSort(array: [ Int ]) -> [ Int...