Reverse a number or an integer in Go (Golang) - Welcome To Golang By Example

Table of Contents

Overview

The objective is to reverse a number that is an integer. Integer can be negative as well. Some examples

Input: 123
Output: 321

Input: 140
Output: 41

Input: -123
Output: -321

Input: 0
Output: 0

Here is the strategy

First, make the input number positive

Use the below logic to iterate over the number and get the last digit every time. Use the last digit to create the reversedDigit

for x > 0 {
	lastDigit := x % 10
	reversedDigit = reversedDigit*10 + lastDigit

	x = x / 10
}

Here is the complete program for the same.

Program

package main

import (
	"fmt"
	"math"
)

func main() {
	reversedInteger := reverse(123)
	fmt.Println(reversedInteger)

	reversedInteger = reverse(140)
	fmt.Println(reversedInteger)

	reversedInteger = reverse(-123)
	fmt.Println(reversedInteger)

	reversedInteger = reverse(0)
	fmt.Println(reversedInteger)
}

func reverse(x int) int {
	sign := "positive"
	if x >= 0 {
		sign = "positive"
	} else {
		sign = "negative"
	}

	x = int(math.Abs(float64(x)))

	var reversedDigit int

	for x > 0 {
		lastDigit := x % 10
		reversedDigit = reversedDigit*10 + lastDigit

		x = x / 10
	}

	if sign == "negative" {
		reversedDigit = reversedDigit * -1
	}
	return reversedDigit
}

Output

golang