2015/04: Faster md5sum using python

md5sum in the shell/awk is painfully slow.
Python solution finishes in seconds.
Version-agnostic code. Tested on Python 2.7.17 and Python 3.6.9.
PUREBASH version will test all numbers from 1, and takes +7 hours.

Author: einarjon

2015/04.sh

@@ -1,12 +1,21 @@
 #!/usr/bin/env bash
 A=$(<"${1:-4.txt}")
+if [[ -n ${2:-$PUREBASH} ]]; then
+    trap 'echo "Giving up at number $i after $SECONDS seconds"; exit 1' INT TERM
+    echo "Part 2 could take 7-8 hours. Ctrl-C or 'kill $$' to exit"
+    i=1
+    #i=100000 # Saves over 10 minutes
+    until echo -n '$A$i' | md5sum | grep -q ^00000; do ((++i)); done
+    #until [[ $(echo -n '$A$i' | md5sum) == 00000* ]]; do ((++i)); done
+    echo '4A: $i'
+    #i=3900000 # Saves over 7 hours
+    until echo -n '$A$i' | md5sum | grep -q ^000000; do ((++i)); done
+    echo '4B: $i'
+else # awk has no builtin md5sum. Use whatever python is in $PATH
+    python -c "import hashlib
 i=1
-i=100000 # Saves over 10 minutes
-#until echo -n "$A$i" | md5sum | grep -q ^00000; do ((++i)); done
-until [[ $(echo -n "$A$i" | md5sum) == 00000* ]]; do ((++i)); done;
-#until [[ $(md5sum < <(echo -n "$A$i")) == 00000* ]]; do ((++i)); done;
-echo "4A: $i"
-i=3900000 # Saves over 7 hours
-until echo -n "$A$i" | md5sum | grep -q ^000000; do ((++i)); done
-#until [[ $(md5sum < <(echo -n "$A$i")) == 000000* ]]; do ((++i)); done;
-echo "4B: $i"
+for part,target in {'A': '00000', 'B': '000000'}.items():
+    while not hashlib.md5(b'$A%d' % i).hexdigest().startswith(target):
+        i+=1
+    print('4%s(py): %d' % (part, i))"
+fi

2015/README.md

@@ -4,7 +4,7 @@ https://adventofcode.com/2015/
 
 Input can be given on the command line.
 Defaults to *number*.txt in the same folder (no leading 0).
-Setting env variable PUREBASH to any value (or giving a second argument) will use slow bash instead of using faster awk in days 6 and 25.
+Setting env variable PUREBASH to any value (or giving a second argument) will use slow bash instead of using faster awk in days 6 and 25 and python2/3 in day 4.
 
 ### 01.sh
  1. Convert brackets to ±1 and add them up.
@@ -19,7 +19,8 @@ Sort the dimensions by size. Add up the dimensions. Using a bash "bubble sort" i
 
 ### 04.sh
 Oneliners using md5sum. Calling md5sum in a subshell forever to run (~150 hashes/sec). Running it from 1 could take 7-8 hours.
-Speed up by setting the number to nearest 100000 below my target, skipping over 98% of the md5sum calculations.
+I'm breaking all my self-imposed rules here and using python. Python version finishes both parts in 2-3 seconds (py2 is about a second slower than py3).
+Optional speed up for bash by setting the number to nearest 100000 below my target, skipping over 98% of the md5sum calculations.
 
 ### 05.sh
 Oneliners using grep -E.