Added comments for day 2, puzzle b

02b.py

@@ -9,24 +9,42 @@ def main(lines):
 		There's an easy but expensive way to do this. I'll start with that
 		and see if I can refine it later.
 	"""
-	
-	for i, line in enumerate(lines):
-		if i + 1 != len(lines):
-			for word in lines[(i+1):]:
-				diffs = 0
-				idx = 0
-				for j in range(len(line)):
-					if line[j] != word[j]:
-						diffs += 1
-						idx = j
-				if diffs == 1:
-					print("Found a match: {} and {}".format(line, word))
-					print("Matched value: {}".format("".join([word[:idx],word[(idx+1):]])))
+	# Testing a new implementation (should be O(n log n))
+	#
+	# lines.sort()
+	# for i, line in enumerate(lines):
+	# 	if i + 1 != len(lines):
+	# 		word = lines[i+1]
+	# 		diffs = 0
+	# 		idx = 0
+	# 		for j in range(len(line)):
+	# 			if line[j] != word[j]:
+	# 				diffs += 1
+	# 				idx = j
+	# 		if diffs == 1:
+	# 			print("Found a match: {} and {}".format(line, word))
+	# 			print("Matched value: {}".format("".join([word[:idx],word[(idx+1):]])))
+	# 			return
+
+	# Original implementation kept for reference (O(n^2))
+	#
+	for i, line in enumerate(lines): # enumerate gives us an index and the value at that index
+		if i + 1 != len(lines): # don't overflow the list
+			for word in lines[(i+1):]: # only check lines further down the list
+				diffs = 0 # track the number of differences between lines
+				idx = 0 # track the index of the most recent difference
+				for j in range(len(line)): # iterate over the length of a word (they're all the same length)
+					if line[j] != word[j]: # if this character in the first word is different from the same character in the second
+						diffs += 1 # increment the number of differences by 1
+						idx = j # set the difference index equal to the current iteration index
+				if diffs == 1: # if we only found one difference
+					print("Found a match: {} and {}".format(line, word)) # print the matched words
+					print("Matched value: {}".format("".join([word[:idx],word[(idx+1):]]))) # print the matching (NOT non-matching) letters
 					return
 
 if __name__ == "__main__":
-	lines = []
-	with open("02in.txt","r") as f:
-		for line in f:
-			lines.append(line.strip())
-	main(lines)
+	lines = [] # an empty list for the lines in the input file
+	with open("02in.txt","r") as f: # open the file. "with" means we don't have to close it
+		for line in f: # iterate over the lines in the input file
+			lines.append(line.strip()) # strip the newline character, then add it to the list
+	main(lines) # and pass the list to our main function.