84 lines
1.4 KiB
Go
84 lines
1.4 KiB
Go
package fifteen
|
|
|
|
import (
|
|
"bufio"
|
|
"fmt"
|
|
"os"
|
|
"strconv"
|
|
"strings"
|
|
)
|
|
|
|
type game struct {
|
|
starting []int
|
|
numbers []int
|
|
spoken map[int]int
|
|
lastIndex map[int]int
|
|
}
|
|
|
|
func (g *game) load(filename string) error {
|
|
file, err := os.Open(filename)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
defer file.Close()
|
|
|
|
scanner := bufio.NewScanner(file)
|
|
for scanner.Scan() {
|
|
input := strings.Split(scanner.Text(), ",")
|
|
|
|
for _, i := range input {
|
|
v, err := strconv.Atoi(i)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
g.starting = append(g.starting, v)
|
|
}
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
func (g *game) valueAt(index int) int {
|
|
g.spoken = make(map[int]int, index)
|
|
g.lastIndex = make(map[int]int, index)
|
|
for i, n := range g.starting {
|
|
if i != len(g.starting)-1 {
|
|
g.spoken[n]++
|
|
}
|
|
g.lastIndex[n] = i
|
|
g.numbers = append(g.numbers, n)
|
|
}
|
|
|
|
for i := len(g.starting); i < index; i++ {
|
|
last := g.numbers[i-1]
|
|
g.spoken[last]++
|
|
lastIndex := g.lastIndex[last]
|
|
g.lastIndex[last] = i - 1
|
|
|
|
next := 0
|
|
|
|
if g.spoken[last] > 1 {
|
|
next = i - 1 - lastIndex
|
|
}
|
|
|
|
g.numbers = append(g.numbers, next)
|
|
}
|
|
|
|
if len(g.numbers) != index {
|
|
return -1
|
|
}
|
|
|
|
return g.numbers[index-1]
|
|
}
|
|
|
|
// PartOne What is the 2020th number given my input
|
|
func PartOne() string {
|
|
g := game{}
|
|
if err := g.load("fifteen/input.txt"); err != nil {
|
|
return err.Error()
|
|
}
|
|
|
|
return fmt.Sprintf("The 2020th number is %d", g.valueAt(2020))
|
|
}
|