palindrome.go

package main

import (
	"fmt"
	"strconv"
)

// Write a function that takes an integer as an input and return the next number that is a palindrome.

func main() {
	numbers := []int{
		9,
		10,
		11,
		120,
		121,
		12220,
		12221,
		1200,
		12000,
		122222,
		12222,
		1200700022,
		1200770022,
		1222221,
	}

	for _, v := range numbers {
		fmt.Printf("Next palindrome of %d is %d\n", v, palindrome(v))
	}
}

func palindrome(input int) int {
	if input < 10 {
		return 11
	}

	strInput := strconv.Itoa(input)
	length := len(strInput) / 2

	var middle string
	if len(strInput)%2 != 0 {
		middle = strInput[length : length+1]
	}

	left := strInput[0:length]
	right := Reverse(left)
	output := left + middle + right

	intOutput, _ := strconv.Atoi(output)
	if input < intOutput {
		return intOutput
	}

	if middle == "" {
		intLeft, _ := strconv.Atoi(left)
		left = strconv.Itoa(intLeft + 1)
	} else {
		intMiddle, _ := strconv.Atoi(middle)
		middle = strconv.Itoa(intMiddle + 1)
	}

	output = left + middle + Reverse(left)
	intOutput, _ = strconv.Atoi(output)
	return intOutput
}

func Reverse(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}

	return string(runes)
}