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main.go
82 lines (63 loc) · 2 KB
/
main.go
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package main
import (
"log"
"os"
"strconv"
"github.com/TomasCruz/projecteuler"
)
/*
Problem 55; Lychrel numbers
If we take 47, reverse and add, 47 + 74 = 121, which is palindromic.
Not all numbers produce palindromes so quickly. For example,
349 + 943 = 1292,
1292 + 2921 = 4213
4213 + 3124 = 7337
That is, 349 took three iterations to arrive at a palindrome. Although no one has proved it yet,
it is thought that some numbers, like 196, never produce a palindrome. A number that never forms a palindrome
through the reverse and add process is called a Lychrel number. Due to the theoretical nature of these numbers,
and for the purpose of this problem, we shall assume that a number is Lychrel until proven otherwise.
In addition you are given that for every number below ten-thousand, it will either
(i) become a palindrome in less than fifty iterations, or,
(ii) no one, with all the computing power that exists, has managed so far to map it to a palindrome.
In fact, 10677 is the first number to be shown to require over fifty iterations before producing a palindrome:
4668731596684224866951378664 (53 iterations, 28-digits).
Surprisingly, there are palindromic numbers that are themselves Lychrel numbers; the first example is 4994.
How many Lychrel numbers are there below ten-thousand?
*/
func main() {
var limit int
if len(os.Args) > 1 {
limit64, err := strconv.ParseInt(os.Args[1], 10, 64)
if err != nil {
log.Fatal("bad argument")
}
limit = int(limit64)
} else {
limit = 10000
}
projecteuler.Timed(calc, limit)
}
func calc(args ...interface{}) (result string, err error) {
limit := args[0].(int)
result64 := int64(0)
for i := 1; i < limit; i++ {
if isLychrel(i) {
result64++
}
}
result = strconv.FormatInt(result64, 10)
return
}
func isLychrel(x int) bool {
num := projecteuler.MakeBigIntFromInt(x)
arg := num.Clone()
for i := 1; i < 50; i++ {
argRev := arg.Clone()
argRev.ReverseDigits()
arg.AddTo(*argRev)
if arg.IsPalindrome() {
return false
}
}
return true
}