From cd41685cb52eba79f0b87c7c10c623b1a85a0c3f Mon Sep 17 00:00:00 2001
From: Bruno Raoult <braoult@gmail.com>
Date: Sat, 8 Oct 2022 21:29:47 +0200
Subject: [PATCH] Day 23 (bash) part 2 (~7mn run)

---
 2020/RESULTS.txt                     | 12 +++++++
 2020/day21/OUTPUT                    |  8 -----
 2020/day23/README                    |  6 ++--
 2020/day23/{EXAMPLE.txt => TEST.txt} |  0
 2020/day23/ex2.bash                  | 50 ++++++++++++++++++++++++++++
 5 files changed, 66 insertions(+), 10 deletions(-)
 delete mode 100644 2020/day21/OUTPUT
 rename 2020/day23/{EXAMPLE.txt => TEST.txt} (100%)
 create mode 100755 2020/day23/ex2.bash

diff --git a/2020/RESULTS.txt b/2020/RESULTS.txt
index e3a0e93..2b321fb 100644
--- a/2020/RESULTS.txt
+++ b/2020/RESULTS.txt
@@ -485,3 +485,15 @@ ex1.bash: res=31314
 ex2.bash: res=32760
 	time: 1:21.92 real, 81.89 user, 0.01 sys
 	context-switch:	462+1, page-faults: 0+5135
+
+=========================================
+================= day23 =================
+=========================================
+
+ex1.bash: res=75893264
+	time: 0:00.01 real, 0.01 user, 0.00 sys
+	context-switch:	0+1, page-faults: 0+166
+
+ex2.bash: res=38162588308
+	time: 6:52.50 real, 412.30 user, 0.14 sys
+	context-switch:	2219+1, page-faults: 0+30233
diff --git a/2020/day21/OUTPUT b/2020/day21/OUTPUT
deleted file mode 100644
index 435e18d..0000000
--- a/2020/day21/OUTPUT
+++ /dev/null
@@ -1,8 +0,0 @@
-ex1.bash: res=2211
-	time: 0:01.72 real, 1.71 user, 0.00 sys
-	context-switch:	9+1, page-faults: 0+1090
-
-ex2.bash: res=vv,nlxsmb,rnbhjk,bvnkk,ttxvphb,qmkz,trmzkcfg,jpvz
-	time: 0:01.75 real, 1.74 user, 0.00 sys
-	context-switch:	36+4, page-faults: 0+1388
-
diff --git a/2020/day23/README b/2020/day23/README
index 53a52cc..75d1580 100644
--- a/2020/day23/README
+++ b/2020/day23/README
@@ -75,8 +75,6 @@ After the crab is done, what order will the cups be in? Starting after the cup l
 Using your labeling, simulate 100 moves. What are the labels on the cups after cup 1?
 
 Your puzzle answer was 75893264.
-
-The first half of this puzzle is complete! It provides one gold star: *
 --- Part Two ---
 
 Due to what you can only assume is a mistranslation (you're not exactly fluent in Crab), you are quite surprised when the crab starts arranging many cups in a circle on your raft - one million (1000000) in total.
@@ -90,3 +88,7 @@ The crab is going to hide your stars - one each - under the two cups that will e
 In the above example (389125467), this would be 934001 and then 159792; multiplying these together produces 149245887792.
 
 Determine which two cups will end up immediately clockwise of cup 1. What do you get if you multiply their labels together?
+
+Your puzzle answer was 38162588308.
+
+Both parts of this puzzle are complete! They provide two gold stars: **
diff --git a/2020/day23/EXAMPLE.txt b/2020/day23/TEST.txt
similarity index 100%
rename from 2020/day23/EXAMPLE.txt
rename to 2020/day23/TEST.txt
diff --git a/2020/day23/ex2.bash b/2020/day23/ex2.bash
new file mode 100755
index 0000000..5fee486
--- /dev/null
+++ b/2020/day23/ex2.bash
@@ -0,0 +1,50 @@
+#!/bin/bash
+#
+# ex2.bash: Advent2020 game, day 23/game 2.
+
+CMD=${0##*/}
+shopt -s extglob
+set -o noglob
+
+declare -A next                                   # next[i] is cup right to i (ring)
+declare -i end runs cup _cup
+
+read -r str
+tmp="${str//?()/x}"
+tmp=${tmp#x}
+IFS=x read -ra array <<< "$tmp"
+
+cup=${array[0]}
+end=1000000
+runs=10000000
+
+_cup=$cup
+# initialize the next array with input cups
+for _next in "${array[@]:1}"; do
+    next[$_cup]=$_next
+    _cup=$_next
+done
+# initialize the next array (up to end)
+for ((_next = 10; _next <= end; ++_next)); do
+    next[$_cup]=$_next
+    _cup=$_next
+done
+next[$_cup]=$cup                                  # close the ring
+
+_cup=$cup
+declare -i _1st _2nd _3rd dest
+for ((i = 1; i <= runs; ++i)); do
+    _1st="${next[$cup]}"
+    _2nd="${next[$_1st]}"
+    _3rd="${next[$_2nd]}"
+    dest=$cup
+    while
+        (( --dest > 0 )) || dest=$end
+        (( dest == _1st || dest == _2nd || dest == _3rd ))
+    do :; done
+    (( tmp=next[$dest], next[$dest]=_1st, next[$cup]=next[$_3rd], next[$_3rd]=tmp ))
+    (( cup=next[$cup] ))
+done
+
+printf "%s: res=%d\n" "$CMD" $(( next[1] * next[${next[1]}] ))
+exit 0