Part 1 for day 21.

2017/day-21/solution.coffee

@@ -0,0 +1,81 @@
+String.prototype.count = (pattern) ->
+	(this.match(pattern) || []).length
+
+stdin = process.openStdin()
+
+stdin.setEncoding 'utf8'
+
+data = ''
+
+stdin.on 'data', (input) ->
+	data += input
+
+stdin.on 'end', () ->
+	mappings = {}
+
+	rotate = (line) ->
+		rows = line.split '/'
+
+		newrows = []
+
+		len = rows.length
+
+		for i in [0...len]
+			newrows[i] = ''
+			for j in [0...len]
+				newrows[i] += rows[rows.length - 1 - j].substr i, 1
+
+		newrows.join '/'
+
+	flip = (line) ->
+		(row.split('').reverse().join '' for row in line.split '/').join '/'
+
+	view = (state) ->
+		console.log state.split('/').join "\n"
+
+	for line in data.trim().split('\n')
+		do (line) ->
+		[source, enhanced] = line.split ' => '
+
+		for i in [1..4]
+			mappings[source] = enhanced
+			mappings[flip source] = enhanced
+			source = rotate source
+
+	state = '.#./..#/###'
+	view state
+
+	for _ in [1..5]
+		newrows = []
+		oldrows = state.split '/'
+
+		if oldrows.length % 2 == 0
+			for i in [0...(oldrows.length / 2)]
+				currows = ['', '', '']
+
+				for j in [0...(oldrows.length / 2)]
+					curblock = (oldrows[2 * i].substr 2 * j, 2) + '/' + (oldrows[2 * i + 1].substr 2 * j, 2)
+					blockrows = mappings[curblock].split '/'
+
+					for r in [0..2]
+						currows[r] += blockrows[r]
+
+				for row in currows
+					newrows.push row
+		else
+			for i in [0...(oldrows.length / 3)]
+				currows = ['', '', '', '']
+
+				for j in [0...(oldrows.length / 3)]
+					curblock = (oldrows[3 * i].substr 3 * j, 3) + '/' + (oldrows[3 * i + 1].substr 3 * j, 3) + '/' + (oldrows[3 * i + 2].substr 3 * j, 3)
+					blockrows = mappings[curblock].split '/'
+
+					for r in [0..3]
+						currows[r] += blockrows[r]
+
+				for row in currows
+					newrows.push row
+
+		state = newrows.join '/'
+		console.log(state.count(/#/g))
+		view state