From 870070aff7babc540844cff6e6d162dd9c5280ac Mon Sep 17 00:00:00 2001
From: Rickard Natt och Dag <rickard@nattochdag.dev>
Date: Fri, 20 Dec 2024 09:25:09 +0100
Subject: [PATCH] feat(2024): parallelize day 20 for performance

---
 go/2024/README.md             |  3 ++-
 go/2024/puzzles/day20/main.go | 30 ++++++++++++++++++++++--------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/go/2024/README.md b/go/2024/README.md
index 910d7bb..759638e 100644
--- a/go/2024/README.md
+++ b/go/2024/README.md
@@ -60,7 +60,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 | 17  |     13964 ns/op |     561424 ns/op |                     |
 | 18  |    755414 ns/op |    1996995 ns/op |                     |
 | 19  |  16126963 ns/op |   16206756 ns/op |                     |
-| 20  | 762519479 ns/op |  845552729 ns/op |                     |
+| 20  | 762519479 ns/op |  845552729 ns/op | `85.99%` / `63.78%` |
 
 \* compared to first solution
 
@@ -80,6 +80,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 |  12 |  10984420 ns/op |    16856988 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/7a220ed0e6deae74d0a293615e6348e6ce1a9a22/go/2024/puzzles/day12/main.go) |
 |  13 |   2900453 ns/op |      702380 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/0cf31064eb05f384cebe45cbeaf80ba90e0947ce/go/2024/puzzles/day13/main.go) |
 |  14 |    594981 ns/op |    56488050 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/a3f28eb2691d3e4be60ec56ab7f699332a2b3d31/go/2024/puzzles/day14/main.go) |
+|  20 | 762519479 ns/op |   845552729 ns/op |                     | [Link](https://github.com/believer/advent-of-code/blob/305eba9ced6b40ecce606cf19f7cb9fc00e5ed73/go/2024/puzzles/day20/main.go) |
 
 ## Running
 
diff --git a/go/2024/puzzles/day20/main.go b/go/2024/puzzles/day20/main.go
index 0c86529..6b9b3dd 100644
--- a/go/2024/puzzles/day20/main.go
+++ b/go/2024/puzzles/day20/main.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"sync"
 
 	"github.com/believer/aoc-2024/utils/files"
 	"github.com/believer/aoc-2024/utils/grid"
@@ -58,19 +59,32 @@ func race(name string, maxCheatTime int) int {
 		}
 	}
 
+	var mu sync.Mutex
+	var wg sync.WaitGroup
+
 	for p := range distances {
-		for p2 := range distances {
-			d := p.ManhattanDistance(p2)
+		wg.Add(1)
 
-			if d > maxCheatTime {
-				continue
-			}
+		go func(p grid.Point) {
+			defer wg.Done()
+
+			for p2 := range distances {
+				d := p.ManhattanDistance(p2)
 
-			if distances[p2]-distances[p]-d >= 100 {
-				cheats++
+				if d > maxCheatTime {
+					continue
+				}
+
+				if distances[p2]-distances[p]-d >= 100 {
+					mu.Lock()
+					cheats++
+					mu.Unlock()
+				}
 			}
-		}
+		}(p)
 	}
 
+	wg.Wait()
+
 	return cheats
 }