From 9a95effede4e0f03b7669d14f39c45356b19e7f7 Mon Sep 17 00:00:00 2001
From: sejo <compudanzas@posteo.net>
Date: Fri, 15 Dec 2023 06:51:19 +0100
Subject: [PATCH] day 15! parts 1 and 2

---
 12023/15/15.lua | 60 +++++++++++++++++++++++++++++++++++++++++++++++++
 12023/15/test   |  1 +
 2 files changed, 61 insertions(+)
 create mode 100644 12023/15/15.lua
 create mode 100644 12023/15/test

diff --git a/12023/15/15.lua b/12023/15/15.lua
new file mode 100644
index 0000000..76f0682
--- /dev/null
+++ b/12023/15/15.lua
@@ -0,0 +1,60 @@
+io.input("input")
+
+function hash(s)
+    local curr = 0
+    local bytes = table.pack(s:byte(1,#s))
+
+    for i,v in ipairs(bytes) do
+        curr = curr + v
+        curr = curr*17
+        curr = curr%256
+    end
+    return curr
+end
+
+local line = io.read()
+local sum1 = 0
+
+function box_contains_label(b, label)
+    if not b or #b==0 then return nil end
+    for i,lens in pairs(b) do
+        local lab, flen = table.unpack(lens)
+        if lab==label then return i end
+    end
+    return nil
+end
+
+local boxes = {}
+for step in line:gmatch("([^%,]+)") do
+    local h = hash(step)
+    sum1 = sum1 + h
+
+    local label,op,focal_length = step:match("([%a]+)([%p])([%d]*)")
+    local bxn = hash(label)
+    local index = box_contains_label(boxes[bxn], label)
+    if op=="=" then
+        if not boxes[bxn] then boxes[bxn] = {} end
+        if not index then 
+            table.insert(boxes[bxn], table.pack(label, focal_length))
+        else
+            boxes[bxn][index] = table.pack(label, focal_length)
+        end
+    else -- "-"
+        if index then
+            table.remove(boxes[bxn], index)
+        end
+    end
+end
+print("part 1", sum1)
+
+local sum2 = 0
+for i,b in pairs(boxes) do
+    --print("BOX",i)
+    for j,s in ipairs(b) do
+        local fpower = (i+1)*j*s[2]
+        --print(j,table.concat(s,"->"),fpower)
+        sum2 = sum2 + fpower
+    end
+end
+
+print("part 2", sum2)
diff --git a/12023/15/test b/12023/15/test
new file mode 100644
index 0000000..62f7ed0
--- /dev/null
+++ b/12023/15/test
@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7
\ No newline at end of file