From 1f7108be477604910a903392b0c552b89a4b8535 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 3 Feb 2025 23:02:24 +0100
Subject: [PATCH] Euclid's algorithm

---
 2024/bonus/day08/freq/pair/main.tf | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/2024/bonus/day08/freq/pair/main.tf b/2024/bonus/day08/freq/pair/main.tf
index ffbd3b4..408034a 100644
--- a/2024/bonus/day08/freq/pair/main.tf
+++ b/2024/bonus/day08/freq/pair/main.tf
@@ -17,6 +17,24 @@ variable "height" {
 locals {
   dx = var.second[0] - var.first[0]
   dy = var.second[1] - var.first[1]
+
+  sorted = abs(local.dx) < abs(local.dy) ? [abs(local.dx), abs(local.dy)] : [abs(local.dy), abs(local.dx)]
+  gcd0   = local.sorted[0] == 0 ? [0, 1] : local.sorted
+
+  # Do as many iterations as necessary. 
+  gcd1  = local.gcd0[0] == 0 ? local.gcd0 : [local.gcd0[1] % local.gcd0[0], local.gcd0[0]]
+  gcd2  = local.gcd1[0] == 0 ? local.gcd1 : [local.gcd1[1] % local.gcd1[0], local.gcd1[0]]
+  gcd3  = local.gcd2[0] == 0 ? local.gcd2 : [local.gcd2[1] % local.gcd2[0], local.gcd2[0]]
+  gcd4  = local.gcd3[0] == 0 ? local.gcd3 : [local.gcd3[1] % local.gcd3[0], local.gcd3[0]]
+  gcd5  = local.gcd4[0] == 0 ? local.gcd4 : [local.gcd4[1] % local.gcd4[0], local.gcd4[0]]
+  gcd6  = local.gcd5[0] == 0 ? local.gcd5 : [local.gcd5[1] % local.gcd5[0], local.gcd5[0]]
+  gcd7  = local.gcd6[0] == 0 ? local.gcd6 : [local.gcd6[1] % local.gcd6[0], local.gcd6[0]]
+  gcd8  = local.gcd7[0] == 0 ? local.gcd7 : [local.gcd7[1] % local.gcd7[0], local.gcd7[0]]
+  gcd9  = local.gcd8[0] == 0 ? local.gcd8 : [local.gcd8[1] % local.gcd8[0], local.gcd8[0]]
+  gcd10 = local.gcd9[0] == 0 ? local.gcd9 : [local.gcd9[1] % local.gcd9[0], local.gcd9[0]]
+
+  # 10 iterations should cover numbers up to 55, which is more than the width/height
+  gcd = local.gcd10[1]
 }
 
 output "nodes1" {
@@ -28,7 +46,7 @@ output "nodes1" {
 
 output "nodes2" {
   value = concat(
-    [for i in range(max(var.width, var.height)) : [var.first[0] - i * local.dx, var.first[1] - i * local.dy]],
-    [for i in range(max(var.width, var.height)) : [var.second[0] + i * local.dx, var.second[1] + i * local.dy]]
+    [for i in range(max(var.width, var.height)) : [var.first[0] - i * local.dx / local.gcd, var.first[1] - i * local.dy / local.gcd]],
+    [for i in range(max(var.width, var.height)) : [var.second[0] + i * local.dx / local.gcd, var.second[1] + i * local.dy / local.gcd]]
   )
 }