cp's OEIS Frontend

Go

package main
import (
    "fmt"
    "math"
)
func main() {
    fmt.Println(a(5))
}
func a(n int) int {
    k := int(math.Pow(10, float64(n))) // get the number of terms of the Kolakoski sequence (A000002) to generate
    // seq stores the Kolakoski sequence
    seq := make([]int, 0, k+1) // n+1 because instruction 2 could add one extra
    var ind, i, toAppend int   // ind represents which instruction to follow
    seq = append(seq, 1, 2, 2) // initial terms
    ind = 2                    // follow third instruction next
    i += 3                     // three numbers already added
    for i < k {
        if seq[ind] == 1 { // add one number?
            if seq[len(seq)-1] == 1 {
                toAppend = 2
            } else {
                toAppend = 1
            }
            seq = append(seq, toAppend)
            i++   // we added a number
            ind++ // next instruction
        } else { // add two numbers
            if seq[len(seq)-1] == 1 {
                toAppend = 2
            } else {
                toAppend = 1
            }
            seq = append(seq, toAppend, toAppend) // append two numbers
            i += 2 // we added two numbers
            ind++
        }
    }
    seq = seq[:k] // trim to k values
    // now count twos
    var twos int
    for _, curr := range seq {
        if curr == 2 {
            twos++
        }
    }
    return twos
}