From d4b47d15a1a837c777c1f155d24d7c3ae111a7c5 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 25 Dec 2020 15:51:05 +0100
Subject: Add day 23

---
 23/a.lua | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 23/a.lua

(limited to '23/a.lua')

diff --git a/23/a.lua b/23/a.lua
new file mode 100644
index 0000000..811ccdc
--- /dev/null
+++ b/23/a.lua
@@ -0,0 +1,63 @@
+input = '716892543'
+cups = {}
+for i = 1, #input do
+    table.insert(cups, tonumber(input:sub(i,i)))
+end
+
+function next_target(n)
+    n = n - 1
+    if n == 0 then
+        n = 9
+    end
+    return n
+end
+
+for round = 1, 100 do
+    current_value = cups[1]
+
+    next_values = {}
+    for i = 2, 4 do
+        next_values[cups[i]] = true
+    end
+
+    target = next_target(current_value)
+    while next_values[target] do
+        target = next_target(target)
+    end
+
+    target_index = 5
+    while cups[target_index] ~= target do
+        target_index = target_index + 1
+    end
+
+    new_cups = {}
+    if target_index ~= 5 then
+        for i = 5, target_index - 1 do
+            table.insert(new_cups, cups[i])
+        end
+    end
+    table.insert(new_cups, target)
+    for i = 2, 4 do
+        table.insert(new_cups, cups[i])
+    end
+    if target_index ~= 9 then
+        for i = target_index + 1, 9 do
+            table.insert(new_cups, cups[i])
+        end
+    end
+    table.insert(new_cups, cups[1])
+    cups = new_cups
+end
+
+one_index = 1
+while cups[one_index] ~= 1 do
+    one_index = one_index + 1
+end
+
+for i = one_index + 1, 9 do
+    io.write(cups[i])
+end
+for i = 1, one_index - 1 do
+    io.write(cups[i])
+end
+print()
-- 
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