From da96bf0fb984fa0fb5a7459e3b195d33207cb0db Mon Sep 17 00:00:00 2001
From: Rokas Puzonas <rokas.puz@gmail.com>
Date: Sun, 22 May 2022 15:19:54 +0000
Subject: [PATCH] feat: solve day 23 part 2

---
 23/main.py | 58 ++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 50 insertions(+), 8 deletions(-)

diff --git a/23/main.py b/23/main.py
index 3a9c2f2..4d12d1e 100644
--- a/23/main.py
+++ b/23/main.py
@@ -23,8 +23,10 @@ def simulate(cups: list[int], moves: int):
 
     current_cup_label = cups[0]
     for _ in range(moves):
+        # take 3 cups
         taken_cups = take_cups(cups, cups.index(current_cup_label)+1, 3)
 
+        # determine destination cup
         destination_label = current_cup_label - 1
         while destination_label not in cups:
             destination_label -= 1
@@ -32,10 +34,40 @@ def simulate(cups: list[int], moves: int):
                 destination_label = max_value
         destination = cups.index(destination_label)
 
+        # put back the 3 taken cups
         put_cups(cups, destination + 1, taken_cups)
 
+        # move current cup
         current_cup_label = cups[(cups.index(current_cup_label) + 1) % len(cups)]
 
+def simulate_lookup(next_cup_lookup: list[int], current_cup: int, moves: int):
+    max_value = len(next_cup_lookup) - 1
+    min_value = 1
+
+    for _ in range(moves):
+        # take 3 cups
+        taken_cup1 = next_cup_lookup[current_cup]
+        taken_cup2 = next_cup_lookup[taken_cup1]
+        taken_cup3 = next_cup_lookup[taken_cup2]
+
+        # determine destination cup
+        destination = current_cup
+        while True:
+            destination -= 1
+            if destination < min_value:
+                destination = max_value
+            if destination != taken_cup1 and destination != taken_cup2 and destination != taken_cup3:
+                break
+
+        # put back the 3 taken cups
+        next_cup_lookup[current_cup] = next_cup_lookup[taken_cup3]
+        after_destination = next_cup_lookup[destination]
+        next_cup_lookup[taken_cup3] = after_destination
+        next_cup_lookup[destination] = taken_cup1
+
+        # move current cup
+        current_cup = next_cup_lookup[current_cup]
+
 def part1(cups: list[int]) -> str:
     simulate(cups, 100)
 
@@ -43,18 +75,28 @@ def part1(cups: list[int]) -> str:
     return "".join(map(str, cups[num1_index+1:])) + "".join(map(str, cups[:num1_index]))
 
 def part2(cups: list[int]) -> int:
-    for value in range(max(cups), 1_000_000 + 1):
-        cups.append(value)
+    # create lookup table for the next value
+    next_cup_lookup: list[int] = [0]*(len(cups)+1)
+    max_value = max(cups)
+    cups.append(max_value+1)
+    for i in range(len(cups)-1):
+        cup = cups[i]
+        next_cup = cups[i+1]
+        next_cup_lookup[cup] = next_cup
 
-    simulate(cups, 1_00)
-    # simulate(cups, 10_000_000)
+    for next_cup in range(max_value+2, 1_000_000+1):
+        next_cup_lookup.append(next_cup)
+    next_cup_lookup.append(cups[0])
 
-    num1_index = cups.index(1)
-    star1 = cups[(num1_index + 1) % len(cups)]
-    star2 = cups[(num1_index + 2) % len(cups)]
+    # perform the simulation
+    simulate_lookup(next_cup_lookup, cups[0], 10_000_000)
+
+    # calculate the final result
+    star1 = next_cup_lookup[1]
+    star2 = next_cup_lookup[star1]
     return star1 * star2
 
 if __name__ == "__main__":
-    cups = read_input("test.txt")
+    cups = read_input("input.txt")
     print("part1: ", part1(cups.copy()))
     print("part2: ", part2(cups.copy()))