day04

day04.sh

@@ -0,0 +1,61 @@
+#!/usr/bin/env bash
+unset PATH; readonly PATH
+source ./utils/main.sh
+
+count_patterns_occurences() {
+  local input="$1"; shift
+  local patterns=("$@") result=0
+
+  for pattern in "${patterns[@]}"; do
+    local text="$input"
+    while [[ -n "$text" ]]; do
+      if [[ "$text" =~ $pattern ]]; then
+        ((result++))
+        text="${text#*"${BASH_REMATCH[0]}"}"
+        text="${BASH_REMATCH[0]:1}$text"
+      else
+        text=''
+      fi
+    done
+  done
+
+  printf '%d' "$result"
+}
+
+p1() {
+  local input="$1" line result=0 cols=0
+
+  read -ra line <<< "$input"
+  cols="$((${#line}+1))"
+
+  local patterns=(
+    "XMAS"
+    "SAMX"
+    "X.{$((cols))}M.{$((cols))}A.{$((cols))}S"
+    "S.{$((cols))}A.{$((cols))}M.{$((cols))}X"
+    "X.{$((cols-1))}M.{$((cols-1))}A.{$((cols-1))}S"
+    "S.{$((cols-1))}A.{$((cols-1))}M.{$((cols-1))}X"
+    "X.{$((cols-2))}M.{$((cols-2))}A.{$((cols-2))}S"
+    "S.{$((cols-2))}A.{$((cols-2))}M.{$((cols-2))}X"
+  )
+
+  count_patterns_occurences "$input" "${patterns[@]}"
+}
+
+p2() {
+  local input="$1" line result=0 cols=0
+
+  read -ra line <<< "$input"
+  cols="$((${#line}+1))"
+
+  local patterns=(
+    "M.M.{$((cols-2))}A.{$((cols-2))}S.S"
+    "M.S.{$((cols-2))}A.{$((cols-2))}M.S"
+    "S.M.{$((cols-2))}A.{$((cols-2))}S.M"
+    "S.S.{$((cols-2))}A.{$((cols-2))}M.M"
+  )
+
+  count_patterns_occurences "$input" "${patterns[@]}"
+}
+
+main "$@"