From 353d5e92c98bf33286f0d32ec68c71d152765a20 Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Tue, 15 Dec 2020 21:41:07 -0500
Subject: [PATCH] performance improvements; no more string conversions or
 lookups in the map

---
 15/main.go | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/15/main.go b/15/main.go
index 0191b3a..4a16246 100644
--- a/15/main.go
+++ b/15/main.go
@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -55,32 +56,30 @@ func partTwo() {
 	// caching implementation. It's still slow, but it at least finishes...!
 	scanner.Scan()
 	numbers := strings.Split(scanner.Text(), ",")
-	seen := make(map[string]int)
+	seen := make(map[int]int)
 
 	// load in numbers
 	for i, v := range numbers[:len(numbers)-1] {
-		seen[v] = i
+		j, _ := strconv.Atoi(v)
+		seen[j] = i
 	}
 
+	i := len(numbers) - 1
+	lastNumber, _ := strconv.Atoi(numbers[i])
 	for {
-		i := len(numbers) - 1
-		lastNumber := numbers[i]
-		if len(numbers) == 30000000 {
-			fmt.Println(numbers[30000000-1])
+		if seen[lastNumber] == 30000000-1 {
+			fmt.Println(lastNumber)
 			return
 		}
-		if v, ok := seen[lastNumber]; !ok {
-			// never seen that before
-			numbers = append(numbers, "0")
-			seen[lastNumber] = i
-			continue
-		} else {
+		if v, ok := seen[lastNumber]; ok {
 			// a number matched; insert the difference between the last number and when we last saw it
-			n := fmt.Sprintf("%d", i-v)
-			numbers = append(numbers, n)
 			seen[lastNumber] = i
-			continue
+			lastNumber = i - v
+		} else {
+			// never seen that before
+			seen[lastNumber] = i
+			lastNumber = 0
 		}
+		i = i + 1
 	}
-
 }