Adding Large Numbers Using Strings in Go | CodeSignal Learn

Adding Large Numbers Using Strings in Go | CodeSignal Learn

Introduction

Hello and welcome! Today, we'll delve deep into a captivating problem involving large numbers — specifically, adding extraordinarily large numbers. As you may have noticed, traditional calculators and even some programming languages struggle when dealing with excessively large numbers. To handle such scenarios efficiently, we'll simulate this process manually using strings. By the end of this discussion, you'll be able to add together numbers that have thousands or even tens of thousands of digits. Intriguing, right? Let's get started!

Task Statement

In today's task, we'll venture into the realm of large numbers, where we are given two exceedingly large positive integers. However, these aren't your average, everyday large numbers. They are so enormous they're represented as strings that can be up to 10,000 digits long! Your mission, should you choose to accept it, is to write a Go function that adds these two "string-numbers" together. The challenge is to perform the addition without converting these entire strings into integers. At the end, your function should return the resulting sum, represented as a string. At first glance, this might seem daunting, but don't worry — we'll break it down step by step, emulating the way we manually add numbers.

Step 1 - Initializing Variables

Before we dive into the code, let's first discuss the strategy we're going to follow. Remember that every digit in a number carries value, and the position of the digit determines its influence on the total value of the number. This system is known as place-value notation. The first step involves initializing our variables. We'll use two int s, i and j, to point to the current digit in num1 and num2, respectively. We'll also need a carry int variable to hold the carryovers from each addition operation. Lastly, we'll use a slice of bytes, named result, to store our resultant number, where each digit from the addition is appended to the front. Go func addLargeNumbers(num1, num2 string) string {i := len(num1) - 1 j := len(num2) - 1 carry := 0 var result []byte We prefer using a slice of bytes over strings.Builder because a slice of bytes allows for efficient insertion of each computed digit at the front, aligning with our right-to-left processing, while strings.Builder only allows appending at the end of the string. This, in turn, simplifies the logic by avoiding the need for additional steps such as reversing the result at the end.

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Step 2 - Scanning and Extracting Digits

After initializing our variables, it's time to move on to the next step. Here, we'll scan through num1 and num2 from right to left, moving from the least significant digit to the most significant one. For each iteration, we extract the digits n1 from num1 and n2 from num2 . If i or j is less than 0, that means we've processed all the digits in one of the numbers. Therefore, we treat any additional digits as 0. The condition carry != 0 ensures that we account for any remaining carry that needs to be added after processing all digits. func addLargeNumbers(num1, num2 string) string {i := len(num1) - 1 j := len(num2) - 1 carry := 0 var result []byte for i >= 0 || j >= 0 || carry != 0 {n1 := 0 if i >= 0 {n1 = int(num1[i] - '0')} n2 := 0 if j >= 0 {n2 = int(num2[j] - '0')} i-- j--

Step 3 - Adding Digits and Finalizing the Result

After obtaining digits n1 and n2, our next step is to add them. This addition also includes the carry, which accumulates any overflow from the addition of previous column digits. This sum results in a one- or two-digit number, where the tens place becomes a new carry and the units place is the result digit. Subsequently, we add current to the result slice and decrement both i and j before starting the next iteration. Finally, we join the result slice of bytes together to obtain our final result. package main import ("fmt") func addLargeNumbers(num1, num2 string) string {i := len(num1) - 1 j := len(num2) - 1 carry := 0 var result []byte for i >= 0 || j >= 0 || carry != 0 {n1 := 0 if i >= 0 {n1 = int(num1[i] - '0')} n2 := 0 if j >= 0 {n2 = int(num2[j] - '0')} current := n1 + n2 + carry carry = current / 10 current = current % 10 result = append([]byte{'0' + byte(current)}, result...) i-- j--} return string(result)} func main() {fmt.Println(addLargeNumbers("1454178195297", "8458263917502")) // Output: 9912442112799}

Go

func addLargeNumbers(num1, num2 string) string {
    i := len(num1) - 1
    j := len(num2) - 1
    carry := 0
    var result []byte

    for i >= 0 || j >= 0 || carry != 0 {
        n1 := 0
        if i >= 0 {
            n1 = int(num1[i] - '0')
        }
        n2 := 0
        if j >= 0 {
            n2 = int(num2[j] - '0')
        }
        i--
        j--

Go

package main

import (
    "fmt"
)

func addLargeNumbers(num1, num2 string) string {
    i := len(num1) - 1
    j := len(num2) - 1
    carry := 0
    var result []byte

    for i >= 0 || j >= 0 || carry != 0 {
        n1 := 0
        if i >= 0 {
            n1 = int(num1[i] - '0')
        }
        n2 := 0
        if j >= 0 {
            n2 = int(num2[j] - '0')
        }

        current := n1 + n2 + carry
        carry = current / 10
        current = current % 10
        result = append([]byte{'0' + byte(current)}, result...)
        i--
        j--
    }

    return string(result)
}

func main() {
    fmt.Println(addLargeNumbers("1454178195297", "8458263917502")) // Output: 9912442112799
}