[Golang] Longest Collatz Sequence - Problem 14 - Project Euler

Go solution to longest Collatz sequence - Problem 14 - Project Euler. [1]

Problem:

The following iterative sequence is defined for the set of positive integers:

n → n/2 (n is even)

n → 3n + 1 (n is odd)

Using the rule above and starting with 13, we generate the following sequence:

13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1

It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1.

Which starting number, under one million, produces the longest chain?

NOTE: Once the chain starts the terms are allowed to go above one million.

Solution:

starting number: 837799, chain length: 525

Run Code on Go Playground

package main

import (
      "fmt"
)

func CollatzSequence(n uint) []uint {
      var result []uint
      result = append(result, n)
      for n != 1 {
              if n%2 == 0 {
                      n /= 2
              } else {
                      n = 3*n + 1
              }
              result = append(result, n)
      }
      return result
}

func main() {
      number := uint(1)
      max := 1
      for n := uint(1); n < 1000000; n++ {
              length := len(CollatzSequence(n))
              if length > max {
                      number = n
                      max = length
              }
      }
      fmt.Println(number)
      fmt.Println(max)
}

Tested on: Go Playground

References: