From 2f6b8a688ef675f113c5a586d5bd64a673b300ce Mon Sep 17 00:00:00 2001
From: Brian Buller <brian@bullercodeworks.com>
Date: Tue, 15 Dec 2020 08:41:00 -0600
Subject: [PATCH] 2020 Day 15 Complete

---
 2020/day14/main.go   |  2 +-
 2020/day15/input     |  1 +
 2020/day15/main.go   | 47 ++++++++++++++++++++++++++++++++++++++++++++
 2020/day15/testinput |  1 +
 4 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 2020/day15/input
 create mode 100644 2020/day15/main.go
 create mode 100644 2020/day15/testinput

diff --git a/2020/day14/main.go b/2020/day14/main.go
index a67a2c1..7b02e65 100644
--- a/2020/day14/main.go
+++ b/2020/day14/main.go
@@ -8,7 +8,7 @@ import (
 )
 
 func main() {
-	fmt.Println("# Day 13")
+	fmt.Println("# Day 14")
 	inp := h.StdinToStringSlice()
 	vsn := h.Atoi(h.OptArgNumber(1, "1"))
 	if vsn == 1 {
diff --git a/2020/day15/input b/2020/day15/input
new file mode 100644
index 0000000..5c1cb85
--- /dev/null
+++ b/2020/day15/input
@@ -0,0 +1 @@
+0,8,15,2,12,1,4
diff --git a/2020/day15/main.go b/2020/day15/main.go
new file mode 100644
index 0000000..9895830
--- /dev/null
+++ b/2020/day15/main.go
@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	fmt.Println("# Day 15")
+	inp := h.StdinToString()
+	fmt.Println("## Part 1")
+	dumbFind(inp, 2020)
+	fmt.Println("## Part 2")
+	dumbFind(inp, 30000000)
+}
+
+func dumbFind(inp string, num int) {
+	start := strings.Split(inp, ",")
+	rem := make(map[int][]int)
+	turn := 1
+	var last int
+	for k := range start {
+		last = h.Atoi(start[k])
+		rem[last] = []int{turn}
+		turn++
+	}
+	for turn <= num {
+		last = speakNext(last, turn, &rem)
+		turn++
+	}
+	fmt.Println("Answer:", last)
+}
+
+func speakNext(prev int, turn int, rem *map[int][]int) int {
+	wrk := *rem
+	if len(wrk[prev]) == 1 {
+		wrk[0] = append(wrk[0], turn)
+		return 0
+	} else {
+		last := wrk[prev][len(wrk[prev])-2]
+		diff := (turn - 1) - last
+		wrk[diff] = append(wrk[diff], turn)
+		return diff
+	}
+}
diff --git a/2020/day15/testinput b/2020/day15/testinput
new file mode 100644
index 0000000..c84ffe7
--- /dev/null
+++ b/2020/day15/testinput
@@ -0,0 +1 @@
+0,3,6