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main.go
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main.go
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package main
import (
"fmt"
"strconv"
"github.com/mbark/advent-of-code-2020/util"
)
var input = `1,0,15,2,10,13`
var testInput = `0,3,6`
var testInput2 = `3,1,2`
func main() {
in := util.ReadInput(input, ",")
var startNrs []int
for _, i := range in {
n, _ := strconv.Atoi(i)
startNrs = append(startNrs, n)
}
fmt.Printf("first %d\n", first(startNrs, 2020))
fmt.Printf("second %d\n", first(startNrs, 30000000))
}
func first(start []int, tillTurn int) int {
var lastNr int
saidAt := make([]int, tillTurn)
for i, nr := range start {
lastNr = nr
if i < len(start)-1 {
saidAt[nr] = i + 1
}
}
var turn = len(start) + 1
for ; turn <= tillTurn; turn++ {
at := saidAt[lastNr]
var n int
if at < 1 {
n = 0
} else {
n = turn - 1 - at
}
saidAt[lastNr] = turn - 1
lastNr = n
}
return lastNr
}