Interview question which I faced during FAANG interview

    Programming question given to me at leetcode.

     Given two strings representing very large integer numbers ("123" , "30") return a string      representing the sum of the two numbers ("153").

    The above question can be rephrased as:-

     

     Add two numbers represented by strings

     

     Sum of two large numbers

     

     Add Two Very Large Number (out of range)

     

     How to add two string numbers

     

     

Solution in Swift programming language:

func add(first: String, second: String) {

        var input1 = first

        var input2 = second

        

        var firstArray = Array(first)

        var secondArray = Array(second)

        

        //both inputs should have same number of characters

        var differenceOfCharacter = 0

        if firstArray.count > secondArray.count {

            differenceOfCharacter = firstArray.count - secondArray.count

            (0..<differenceOfCharacter).forEach { (_) in

                input2 = "0" + input2

            }

        } else {

            differenceOfCharacter = secondArray.count - firstArray.count

            

            (0..<differenceOfCharacter).forEach { (_) in

                input1 = "0" + input1

            }

        }

        

        firstArray = Array(input1)

        secondArray = Array(input2)

        

        var reminder = 0

        var sum = 0

        var sumString = ""

        

        for (index,_) in firstArray.enumerated().reversed() {

            let a = firstArray[index].wholeNumberValue ?? 0

            let b = secondArray[index].wholeNumberValue ?? 0

            

            sum = (a + b + reminder) % 10

            reminder = (a + b) / 10

            sumString = "\(sum)" + sumString

        }

        print(sumString)

        

    }