diff --git a/day13.sh b/day13.sh
new file mode 100644
index 0000000..15b37b6
--- /dev/null
+++ b/day13.sh
@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+unset PATH
+readonly PATH
+source ./utils/main.sh
+source ./utils/array.sh
+
+solve() {
+  local ax="$1" ay="$2" bx="$3" by="$4" px="$5" py="$6" tokens=0
+
+  a="$((px * by - py * bx))"
+  b="$((py * ax - px * ay))"
+  c="$((ax * by - ay * bx))"
+
+  ((a % c == 0 && b % c == 0)) && tokens="$((3 * (a / c) + (b / c)))"
+  echo "$tokens"
+}
+
+do_part() {
+  local offset="$1" ax ay bx by result=0
+
+  while read -r line; do
+    [[ -z "$line" ]] && continue
+    [[ "$line" =~ Button\ A:\ X\+([0-9]*),\ Y\+([0-9]*) ]] && read -r ax ay <<<"${BASH_REMATCH[@]:1}" && continue
+    [[ "$line" =~ Button\ B:\ X\+([0-9]*),\ Y\+([0-9]*) ]] && read -r bx by <<<"${BASH_REMATCH[@]:1}" && continue
+    [[ "$line" =~ Prize:\ X=([0-9]*),\ Y=([0-9]*) ]] && ((result += $(solve "$ax" "$ay" "$bx" "$by" "$((BASH_REMATCH[1] + offset))" "$((BASH_REMATCH[2] + offset))")))
+  done
+
+  printf '%s' "$result"
+
+}
+
+p1() {
+  do_part 0 <<<"$1"
+}
+
+p2() {
+  do_part 10000000000000 <<<"$1"
+}
+
+main "$@"
diff --git a/utils/grid.sh b/utils/grid.sh
new file mode 100644
index 0000000..339766c
--- /dev/null
+++ b/utils/grid.sh
@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+
+declare -a __GRID__PERPENDICULAR_DIRECTIONS=(
+  '1 0'
+  '0 1'
+  '0 -1'
+  '-1 0'
+)
+
+grid.coord_to_index() {
+  local width="$1" x="$2" y="$3"
+  printf '%d' "$((y * width + x))"
+}
+
+grid.index_to_coord() {
+  local width="$1" index="$2"
+  printf '%d %d\n' "$((index % width))" "$((index / width))"
+}
+
+grid.text_to_grid() {
+  local -n __grid_text_to_grid_grid="$1"
+  local text="$2" width=0 height=0 c=0
+
+  __grid_text_to_grid_grid=()
+
+  while read -r line; do
+    ((height++))
+    [[ "$width" ]] && width="${#line}"
+    while IFS= read -rd '' -n 1 char; do
+      [[ "$char" == $'\n' ]] && continue
+      __grid_text_to_grid_grid+=(["$c"]="$char")
+      ((c++))
+    done <<<"$line"
+  done <<<"$text"
+
+  __grid_text_to_grid_grid+=([width]="$width")
+  __grid_text_to_grid_grid+=([height]="$height")
+}
+
+grid.perpendicular_neighbors() {
+  local -n __grid_perpendicular_neighbors_grid="$1"
+  local x="$2" y="$3"
+  
+  for dir in "${__GRID__PERPENDICULAR_DIRECTIONS[@]}"; do
+    local dx dy nx ny
+    read -r dx dy <<<"$dir"
+    nx="$(( x + dx ))"
+    ny="$(( y + dy ))"
+    (( nx >= 0 && nx < __grid_perpendicular_neighbors_grid[width] && ny >= 0 && ny < __grid_perpendicular_neighbors_grid[height] )) || continue
+    printf '%d %d\n'  "$nx" "$ny"
+  done
+}
+
+grid.get() {
+  local -n __grid_get_grid="$1"
+  local x="$2" y="$3" width="${__grid_get_grid[width]}"
+
+  (( x >= 0 && x < __grid_get_grid[width] && y >= 0 && y < __grid_get_grid[height] )) || {
+    echo "($x,$y) is out of bounds for grid of size (${__grid_get_grid[width]},${__grid_get_grid[height]})" >&2
+    return 1
+  }
+
+  printf '%s\n' "${__grid_get_grid["$((y * width + x))"]}"
+}
+
+grid.set() {
+  local -n __grid_set_grid="$1"
+  local x="$2" y="$3" value="$4" width="${__grid_set_grid[width]}"
+
+  (( x >= 0 && x < __grid_set_grid[width] && y >= 0 && y < __grid_set_grid[height] )) || {
+    echo "($x,$y) is out of bounds for grid of size (${__grid_set_grid[width]},${__grid_set_grid[height]})" >&2
+    return 1
+  }
+  __grid_set_grid["$((y * width + x))"]="$value"
+}