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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






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