Add day3 problem + solution

day3/p2.nim

@@ -0,0 +1,91 @@
+import os
+import std/[strutils, enumerate, sets, sequtils]
+
+proc getMostCommon(indices: var HashSet[int], values: var seq[string]): string =
+  var counts = newSeq[int](len(values[0]))
+
+  for index in indices:
+    let binary = values[index]
+    for (i, binVal) in enumerate(binary):
+      counts[i] += (if binVal == '1': 1 else: -1)
+
+  result = newString(counts.len)
+
+  for (i, val) in enumerate(counts):
+    if val > 0: # one is most common, so gamma is one, epsilon is zero
+      result[i] = '1'
+    elif val < 0: # zero is most common, so gamma is zero, epsilon is one
+      result[i] = '0'
+    else: # zero and one are the same commonality
+      result[i] = '1'
+
+proc getLeastCommon(indices: var HashSet[int], values: var seq[string]): string =
+  var counts = newSeq[int](len(values[0]))
+
+  for index in indices:
+    let binary = values[index]
+    for (i, binVal) in enumerate(binary):
+      counts[i] += (if binVal == '1': 1 else: -1)
+
+  result = newString(counts.len)
+
+  for (i, val) in enumerate(counts):
+    if val > 0: # one is most common, so gamma is one, epsilon is zero
+      result[i] = '0'
+    elif val < 0: # zero is most common, so gamma is zero, epsilon is one
+      result[i] = '1'
+    else: # zero and one are the same commonality
+      result[i] = '0'
+
+proc main() =
+  let fileName = paramStr(1)
+
+  # if we have a one, increase the counter
+  # otherwise for zero, decrease the counter for each bit
+  # this will give a positive number for 1 being the most
+  # common, and negative if 0 is the most common
+
+  var binarySeq = newSeq[string]()
+
+  for binary in fileName.lines:
+    binarySeq.add(binary)
+
+  var o2Indices = toHashSet(toSeq(0..<binarySeq.len))
+  var co2Indices = toHashSet(toSeq(0..<binarySeq.len))
+
+  var pos = 0
+  while o2Indices.len > 1:
+    var mostCommon = o2Indices.getMostCommon(binarySeq)
+    if pos >= mostCommon.len:
+      break
+    let mc = mostCommon[pos]
+    var o2Copy = o2Indices
+    for index in o2Copy:
+      let binVal = binarySeq[index][pos]
+      if binVal != mc and o2Indices.len > 1:
+        o2Indices.excl(index)
+
+    pos += 1
+
+  pos = 0
+  while co2Indices.len > 1:
+    var leastCommon = co2Indices.getLeastCommon(binarySeq)
+    if pos >= leastCommon.len:
+      break
+    let lc = leastCommon[pos]
+    var co2Copy = co2Indices
+    for index in co2Copy:
+      let binVal = binarySeq[index][pos]
+      if binVal != lc and co2Indices.len > 1:
+        co2Indices.excl(index)
+
+    pos += 1
+
+  let oxygen = binarySeq[o2Indices.toSeq[0]]
+  let co2 = binarySeq[co2Indices.toSeq[0]]
+
+  let lifeSupport = oxygen.parseBinInt * co2.parseBinInt
+  echo "Life support rating: ", lifeSupport
+
+
+main()