From bdba3a22681096a94c7dab9b7b554046d1251e78 Mon Sep 17 00:00:00 2001
From: Brian Buller <brian@bullercodeworks.com>
Date: Thu, 28 Dec 2023 10:46:00 -0600
Subject: [PATCH] 2023 Day 24 Complete!

---
 2023/day24/main.go | 51 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/2023/day24/main.go b/2023/day24/main.go
index 7a81ffd..939861d 100644
--- a/2023/day24/main.go
+++ b/2023/day24/main.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+	"golang.org/x/exp/slices"
 )
 
 func main() {
@@ -43,7 +44,6 @@ func part2(inp []string) {
 	fmt.Println(findThrow(all))
 }
 
-// https://github.com/rumkugel13/AdventOfCode2023/blob/main/day24.go#L139
 func findThrow(all []*hailstone) int {
 	maybeX, maybeY, maybeZ := []int{}, []int{}, []int{}
 	for i := 0; i < len(all)-1; i++ {
@@ -51,10 +51,59 @@ func findThrow(all []*hailstone) int {
 			a, b := all[i], all[j]
 			if a.DX == b.DX {
 				nextMaybe := findMatchingVelocity(int(b.X-a.X), int(a.DX))
+				if len(maybeX) == 0 {
+					maybeX = nextMaybe
+				} else {
+					maybeX = getIntersect(maybeX, nextMaybe)
+				}
+			}
+			if a.DY == b.DY {
+				nextMaybe := findMatchingVelocity(int(b.Y-a.Y), int(a.DY))
+				if len(maybeY) == 0 {
+					maybeY = nextMaybe
+				} else {
+					maybeY = getIntersect(maybeY, nextMaybe)
+				}
+			}
+			if a.DZ == b.DZ {
+				nextMaybe := findMatchingVelocity(int(b.Z-a.Z), int(a.DZ))
+				if len(maybeZ) == 0 {
+					maybeZ = nextMaybe
+				} else {
+					maybeZ = getIntersect(maybeZ, nextMaybe)
+				}
 			}
 		}
 	}
+
+	if len(maybeX) == len(maybeY) && len(maybeY) == len(maybeZ) && len(maybeZ) == 1 {
+		rockVel := hailstone{
+			X: float64(maybeX[0]), Y: float64(maybeY[0]), Z: float64(maybeZ[0]),
+		}
+		hailA, hailB := all[0], all[1]
+		mA := (hailA.DY - rockVel.Y) / (hailA.DX - rockVel.X)
+		mB := (hailB.DY - rockVel.Y) / (hailB.DX - rockVel.X)
+		cA := hailA.Y - (mA * hailA.X)
+		cB := hailB.Y - (mB * hailB.X)
+		xPos := (cB - cA) / (mA - mB)
+		yPos := mA*xPos + cA
+		time := (xPos - hailA.X) / (hailA.DX - rockVel.X)
+		zPos := hailA.Z + (hailA.DZ-rockVel.Z)*time
+		return int(xPos + yPos + zPos)
+	}
+	return h.MIN_INT
 }
+
+func getIntersect(a, b []int) []int {
+	result := []int{}
+	for _, val := range a {
+		if slices.Contains(b, val) {
+			result = append(result, val)
+		}
+	}
+	return result
+}
+
 func findMatchingVelocity(diff, vel int) []int {
 	match := []int{}
 	for v := -1000; v < 1000; v++ {