2020 Day 13 Complete!

2020/day13/input

@@ -0,0 +1,2 @@
+1006605
+19,x,x,x,x,x,x,x,x,x,x,x,x,37,x,x,x,x,x,883,x,x,x,x,x,x,x,23,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,x,x,797,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,29

2020/day13/main.go

@@ -0,0 +1,131 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	fmt.Println("# Day 13")
+	inp := h.StdinToStringSlice()
+	if len(inp) != 2 {
+		fmt.Println("Invalid input")
+		return
+	}
+	part1(inp)
+	part2Rework(inp)
+}
+
+func part1(inp []string) {
+	me := h.Atoi(inp[0])
+	pts := strings.Split(inp[1], ",")
+	earliest := h.MAX_INT
+	var earliestBus int
+	for k := range pts {
+		if pts[k] == "x" {
+			continue
+		}
+		bus := h.Atoi(pts[k])
+		div := me / bus
+		wait := (bus * (div + 1)) - me
+		if earliest > wait {
+			earliest = wait
+			earliestBus = bus
+		}
+	}
+	fmt.Println("## Part 1")
+	fmt.Printf("Answer %d\n\n", earliest*earliestBus)
+}
+
+// This may not work with all inputs...
+func part2Rework(inp []string) {
+	pts := strings.Split(inp[1], ",")
+	buses := make(map[int]int)
+	var keys []int
+	for k, v := range pts {
+		if v == "x" {
+			continue
+		}
+		keys = append(keys, k)
+		buses[k] = h.Atoi(v)
+	}
+	for _, v := range buses {
+		if !h.IsPrime(v) {
+			fmt.Println("Not all buses are prime numbers... This solution _may not work_. Or it may still.", h.SHRUG)
+			break
+		}
+	}
+	res := 0
+	mins := buses[keys[0]]
+	for k := 1; k < len(keys); k++ {
+		wrk := keys[k]
+		bus := buses[wrk]
+		for (res+wrk)%bus != 0 {
+			res = res + mins
+		}
+		mins = mins * bus
+	}
+	fmt.Println("## Part 2")
+	fmt.Printf("Answer: %d\n", res)
+}
+
+/*
+           7      13      59      31      19
+1068781    D       .       .       .       .
+1068782    .       D       .       .       .
+1068783    .       .       .       .       .
+1068784    .       .       .       .       .
+1068785    .       .       D       .       .
+1068786    .       .       .       .       .
+1068787    .       .       .       D       .
+1068788    D       .       .       .       D
+
+7  = 0
+13 = 1
+59 = 4
+31 = 6
+19 = 7
+
+*/
+
+// I think this will get there... Eventually... Maybe...
+func part2(inp []string) {
+	pts := strings.Split(inp[1], ",")
+	wrk := make(map[int]int)
+	var keys []int
+	var vals []int
+	var highK, highV int
+	for k := range pts {
+		if pts[k] == "x" {
+			continue
+		}
+		keys = append(keys, k)
+		vals = append(vals, wrk[k])
+		wrk[k] = h.Atoi(pts[k])
+		if wrk[k] > highV {
+			highK = k
+			highV = wrk[k]
+		}
+	}
+	sort.Sort(sort.Reverse(sort.IntSlice(keys)))
+	sort.Sort(sort.Reverse(sort.IntSlice(keys)))
+	target := highV - highK
+	for !checkMap(target, keys, wrk) {
+		target = target + highV
+	}
+
+	fmt.Println("## Part 2")
+	fmt.Printf("Answer: %d\n", target)
+}
+
+func checkMap(target int, keys []int, all map[int]int) bool {
+	for _, k := range keys {
+		if (target+k)%all[k] != 0 {
+			return false
+		}
+	}
+	return true
+}

2020/day13/testinput

@@ -0,0 +1,2 @@
+939
+7,13,x,x,59,x,31,19

2020/day13/testinput2

@@ -0,0 +1,2 @@
+1
+1789,37,47,1889