Palindrome

palindrome.go

package main

import (
	"fmt"
	"math"
)

func int10Pow(pow uint) uint {
	return uint(math.Pow(10, float64(pow)))
}

// returns reversed uint number
func reverse(num uint) uint {
	var res uint
	for num != 0 {
		res = res*10 + num%10
		num = num / 10
	}
	return res
}

// returns palindrome number with specified left half
func construnctNumber(leftHalfNumber, pow uint) uint {
	result := leftHalfNumber * int10Pow(pow)
	return result + reverse(leftHalfNumber)
}

// returns palindrome and multipliers
func getPalindrome(pow uint) (uint, uint, uint) {
	/// when powering n-digit 9-th (999, 9999)  result is always (9...98|0...01).
	// We will set first half of number to 9...97
	half := int10Pow(pow) - 3

	left, right := int10Pow(pow-1), int10Pow(pow)-1

	for {
		constructed := construnctNumber(half, pow)
		for j := left; j <= right; j++ {
			if constructed%uint(j) == 0 {
				del := uint(constructed / j)
				if del >= left && del <= right {
					return constructed, del, j
				}
			}
		}
		half--
	}
}

func main() {
	var pow uint = 3
	palindrome, v1, v2 := getPalindrome(pow)
	fmt.Printf("palindrome from multiplying 2 %v-digit numbers (%v,%v): %v\n", pow, v1, v2, palindrome)
}