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Commit 440cd13

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After another long hiatus, day 18 is done.
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‎2018/day18/eighteen.go‎

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package main
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import (
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"fmt"
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"os"
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"strings"
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)
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func main() {
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// partOne()
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partTwo()
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}
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func partOne() {
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area := area()
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for row := range area {
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fmt.Printf("%c", area[row])
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fmt.Println()
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}
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for range 10 {
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area = changeState(area)
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}
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fmt.Println("After")
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for row := range area {
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fmt.Printf("%c", area[row])
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fmt.Println()
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}
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wood := countChar2D(area, '|')
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lumber := countChar2D(area, '#')
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fmt.Printf("Part 1 : Total resource value: %d\n", wood*lumber)
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}
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func partTwo() {
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area := area()
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lastGen := 0
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visited := map[[50][50]rune]int{}
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// Get the wood and lumber counts for each generation that we're testing to see
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// if we can discover a pattern
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for minutes := 0; minutes < 1000000000; minutes++ {
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area = changeState(area)
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if visited[area] != 0 {
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firstOccurrence := visited[area]
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period := minutes - firstOccurrence // Repeats after X steps
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fmt.Println("Period:", period)
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// Skip the minutes ahead
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minutes = ((1000000000-firstOccurrence)/period)*period + firstOccurrence
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}
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wood := countChar2D(area, '|')
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lumber := countChar2D(area, '#')
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resources := wood * lumber
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fmt.Printf("For %d Minutes, Total resource value: %d | Diff to previous: %d\n", minutes+1, resources, resources-lastGen)
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lastGen = resources
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visited[area] = minutes
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}
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// The cycle repeats every 28 iterations. The cycle is as follows:
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// For 49972 Minutes, Total resource value: 210824 | Diff to previous: 320
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// For 49973 Minutes, Total resource value: 207282 | Diff to previous: -3542
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// For 49974 Minutes, Total resource value: 205320 | Diff to previous: -1962
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// For 49975 Minutes, Total resource value: 204125 | Diff to previous: -1195
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// For 49976 Minutes, Total resource value: 197316 | Diff to previous: -6809
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// For 49977 Minutes, Total resource value: 192984 | Diff to previous: -4332
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// For 49978 Minutes, Total resource value: 188914 | Diff to previous: -4070
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// For 49979 Minutes, Total resource value: 181485 | Diff to previous: -7429
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// For 49980 Minutes, Total resource value: 177416 | Diff to previous: -4069
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// For 49981 Minutes, Total resource value: 173910 | Diff to previous: -3506
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// For 49982 Minutes, Total resource value: 167475 | Diff to previous: -6435
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// For 49983 Minutes, Total resource value: 164424 | Diff to previous: -3051
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// For 49984 Minutes, Total resource value: 164079 | Diff to previous: -345
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// For 49985 Minutes, Total resource value: 163631 | Diff to previous: -448
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// For 49986 Minutes, Total resource value: 163248 | Diff to previous: -383
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// For 49987 Minutes, Total resource value: 167090 | Diff to previous: 3842
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// For 49988 Minutes, Total resource value: 168562 | Diff to previous: 1472
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// For 49989 Minutes, Total resource value: 171588 | Diff to previous: 3026
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// For 49990 Minutes, Total resource value: 172852 | Diff to previous: 1264
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// For 49991 Minutes, Total resource value: 174900 | Diff to previous: 2048
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// For 49992 Minutes, Total resource value: 176012 | Diff to previous: 1112
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// For 49993 Minutes, Total resource value: 182574 | Diff to previous: 6562
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// For 49994 Minutes, Total resource value: 187272 | Diff to previous: 4698
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// For 49995 Minutes, Total resource value: 193888 | Diff to previous: 6616
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// For 49996 Minutes, Total resource value: 199167 | Diff to previous: 5279
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// For 49997 Minutes, Total resource value: 203648 | Diff to previous: 4481
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// For 49998 Minutes, Total resource value: 204832 | Diff to previous: 1184
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// For 49999 Minutes, Total resource value: 210504 | Diff to previous: 5672
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// ...
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// For 100000 Minutes, Total resource value: 176012 | Diff to previous: 1112
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// Since 1000000000-ひく100000 =わ 999900000
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// 999900000 % 28 = 8
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// We know that at 1 bilion, the iteration will be the 8th, from where the 100000 is currently at.
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// So its the one with the Diff = 320
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// The above was my first solution, which was by hand. I later added a programmatic one, which skips steps ahead.
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wood := countChar2D(area, '|')
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lumber := countChar2D(area, '#')
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fmt.Printf("Part 2 : Total resource value: %d\n", wood*lumber)
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}
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func changeState(area [50][50]rune) [50][50]rune {
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deepCopy := deepCopy(area) // We need an exact copy, so we dont alter the original adjacent values while iterating
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for row := range area {
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for cell, space := range area[row] {
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adjacents := adjacentSquares(area, row, cell) // Get the adjancets from the original
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switch space {
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case '.':
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if n := countChar(adjacents, '|'); n >= 3 {
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deepCopy[row][cell] = '|'
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}
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case '|':
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if n := countChar(adjacents, '#'); n >= 3 {
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deepCopy[row][cell] = '#'
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}
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case '#':
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l := countChar(adjacents, '#')
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t := countChar(adjacents, '|')
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if l == 0 || t == 0 {
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deepCopy[row][cell] = '.'
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}
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}
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}
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}
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return deepCopy
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}
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func adjacentSquares(area [50][50]rune, row, cell int) []rune {
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a := []rune{}
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// Go along all the adjacent squares. be mindfull of edges.
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for i := row - 1; i <= row+1; i++ {
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if i < 0 || i >= len(area) { // Row edges, top and bottom
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continue
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}
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for j := cell - 1; j <= cell+1; j++ {
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if j < 0 || j >= len(area) { // Column edges, left and right
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continue
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}
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if i == row && j == cell { // Dont append the current character were checking
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continue
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}
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a = append(a, area[i][j]) // Append the rest
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}
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}
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return a
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}
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// Count occurrences of any given char.
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func countChar(array []rune, char rune) int {
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c := 0
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for i := range array {
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if array[i] == char {
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c++
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}
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}
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return c
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}
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// Count occurrences of any given char.
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func countChar2D(array [50][50]rune, char rune) int {
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c := 0
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for i := range array {
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for j := range array[i] {
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if array[i][j] == char {
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c++
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}
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}
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}
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return c
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}
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func area() [50][50]rune {
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area := [50][50]rune{}
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f, _ := os.ReadFile("input.txt")
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lines := strings.Split(strings.TrimSpace(string(f)), "\n")
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for i, line := range lines {
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characters := []rune(line)
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copy(area[i][:], characters)
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}
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return area
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}
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func deepCopy(original [50][50]rune) [50][50]rune {
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c := [50][50]rune{}
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for i := range original {
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copy(c[i][:], original[i][:])
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}
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return c
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}

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