add day 1 solution part 1

day03/part1.nim

@@ -0,0 +1,56 @@
+# Copyright 2021 Christian Ulrich
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# usage: ./part1 < input
+
+proc powerConsumption(): uint64 =
+  var
+    line = ""
+    lineCount = 0'u64
+    bitCounts: seq[uint64]
+  while readLine(stdin, line):
+    if line.len() > 0:
+      if line.len() != bitCounts.len():
+        if bitCounts.len() == 0:
+          newSeq(bitCounts, line.len())
+        else:
+          raise newException(ValueError, "invalid line length")
+      lineCount.inc()
+      for index, digit in line.pairs():
+        case digit
+        of '0': discard
+        of '1': bitCounts[index].inc()
+        else: raise newException(ValueError, "invalid digit")
+  var
+    gamma = 0'u64
+    epsilon = 0'u64
+  for index, bitCount in bitCounts.pairs():
+    let bitPosition = bitCounts.len() - 1 - index
+    let mask = 1'u64 shl uint64(bitPosition)
+    if bitCount > lineCount div 2:
+      gamma = gamma or mask
+    else:
+      epsilon = epsilon or mask
+  result = gamma * epsilon
+
+proc main(): int =
+  try:
+    echo powerConsumption()
+  except Exception as error:
+    echo error.msg
+    result = -1
+
+when isMainModule:
+  quit(main())

day03/testinput

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+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010