diff --git a/2020/day-11/index.js b/2020/day-11/index.js
new file mode 100644
index 0000000..af7e035
--- /dev/null
+++ b/2020/day-11/index.js
@@ -0,0 +1,3 @@
+// eslint-disable-next-line no-unused-vars
+const console = require('../helpers')
+require('./solution')
diff --git a/2020/day-11/input.txt b/2020/day-11/input.txt
new file mode 100644
index 0000000..6577da1
--- /dev/null
+++ b/2020/day-11/input.txt
@@ -0,0 +1,91 @@
+LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLL..LLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLL.LL.LLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLL.LLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+...L.L......L...L..L...L..LL.....L.....L..LLLL..L.LL......LL....L..L.L..L....L.LL....LL..L..L
+LLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLLL.LLLLLL.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLL..LLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLL.LLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL..LLLLLLLLLLLLLLLLL.LLLLLLLL.LLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLLLLL.LLLLLLLLLLLLL
+LLLL.LLLLL.LLLL.LLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+.....L.LLLL....LL..L...LLL.L.LL..LL.L........L....LL...L...L...L.LL....LL...L..L.....LL.L....
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LL.LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLL.LL.LLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL..LLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLL.LLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL..LLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLLLLLLLL.LLLLL.LL.LLLLLLLLLL
+...L......L....L....L......L.L.....L..L.L.L..L.L...LLL.....LLLL.L.......LL.LLL.L.LL....L.....
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LL.LLLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.L.LLLL.LLL
+LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LL.L.LLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLLLLLLLL
+...LL..........L..LLLLL...L.L..........L........L.LL..L..L.LLL.L..L.L.....LL...LL....L..L.L..
+LLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLL.LLLL
+LLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLLL..LLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLL.LLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLL.LLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLL..LLLLLLL.LLLLLLLLLL
+LLLLLLLLL..L.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+..LLLL.LL....LLL..L...L..L..L.......L..L...L.L...L..LL.L.L.L.L...L...L.L.L.L.L......LL...L..L
+LLLLLLLLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLL.LLLLLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLL.LLL.LLLLLLLL.L.LLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLLL.LLLLLL..LLLLLL.LLL
+..L...L...L...L..L....L...LL.L.L.L..LL...........LLL.L......L..L.....LL..L..LLL........L....L
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLLLL.LLLLLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLL.LLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLL.LL.LLLL.LLLLLLL.L.LLLLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLL.L.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LL.L.LLLLL
+..L.L.LL....L....L..L....L.L...L..L..L.L.....L..L...L.LL.....L...............L..............L
+LLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LL.L.LLLL.LLL.LLLL.LLLLL.LL.LLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LL.L.LLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLLLL.LL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+L.L.....L.L.L.LL.L......LLL.....L.L.L........L....LL.......L....L.....L....LL..L...LLL......L
+LLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLL.L.LLLL.LLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLL.LLLLLL.LLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL..LLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLL.LLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+...L...L.....L....L.L..........L..L.L..L..L..LL.L..L.......L.......L....L....L...LLL..L..L..L
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLLLLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLL.LLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+..LLL....L.LL....L..............LLL......LL.LLL.....LL..L.L..L........L......L...L.LL..LL..L.
+LLLLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLL.LLL..LLLLLLLLLLLLLL.LLLLLLLLLL
+L.LLLLLLLL.LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLL.LLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLL.LLL...LLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLLLLLLLLLLLL..LLLLLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLL.LLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLLLLLLLLL
+LLLLLLLLLL.LLLL.LLL.LLLLL.LLLLLLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
+L...L.LL......L...LLLLLL.L.L.L...L.L..L..L.LL....L......LL..L...LLL....L...LL......L.........
+LLLLLLLLLL.LLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLL.LLLLLLLLLLLLL.LLLLL.LLLLLLLL.LLLLLLLLLL
+LLLLLLLLLL.LLL..LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLL.LLLLLL.LLLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLL.LLLLLLLLLLLLLLLLLL.LLLLLLL.LLLLLLLLLLLLLLLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLL.LLLLLLLLL.LLLLLLLL.LLLLLLLLLL.LLLLLLLLLLLLLL.LLLL
+LLLLLLLLLLLLLLL.LLLLLLLLL.LLLLLLLLLLLLLLLLL.LLLLLLLLLLLLLLLLLL.LLLL.LLLLLLLLLLLLLL.LLLLLLLLLL
diff --git a/2020/day-11/seating.js b/2020/day-11/seating.js
new file mode 100644
index 0000000..56e750a
--- /dev/null
+++ b/2020/day-11/seating.js
@@ -0,0 +1,112 @@
+
+const parse = (data) => {
+  return data.split('\n').map((row) => {
+    return row.split('')
+  })
+}
+
+const format = (seatMap) => {
+  return seatMap.map((row) => row.join('')).join('\n')
+}
+
+const occupiedLineOfSite = ({ x, y, seatMap }) => {
+  let occupied = 0
+  const look = ({ lookX, lookY, dirX, dirY }) => {
+    if (lookY < 0 || lookY >= seatMap.length) {
+      // exceeded rows space
+      return 'x'
+    }
+    if (lookX < 0 || lookX >= seatMap[0].length) {
+      // exceeded column space
+      return 'x'
+    }
+    // Find the first seat in the direction, recursively
+    if (seatMap[lookY][lookX] !== '.') {
+      return seatMap[lookY][lookX]
+    }
+
+    // Recursively look in the next seat in this direction
+    return look({ lookX: lookX + dirX, lookY: lookY + dirY, dirX, dirY })
+  }
+
+  // 8 compass point directions
+  for (let dirX = -1; dirX <= 1; dirX++) {
+    for (let dirY = -1; dirY <= 1; dirY++) {
+      if (look({ lookX: x + dirX, lookY: y + dirY, dirX, dirY }) === '#') {
+        occupied++
+      }
+    }
+  }
+
+  return occupied
+}
+
+const occupiedNearby = ({ x, y, seatMap }) => {
+  let temp = ''
+
+  for (let row = y - 1; row <= y + 1; row++) {
+    for (let col = x - 1; col <= x + 1; col++) {
+      try {
+        temp += seatMap[row][col] || '-'
+      } catch {
+        temp += '-'
+      }
+    }
+    temp += '\n'
+  }
+  const occupied = (temp.match(/#/g) || []).length
+
+  // console.debug(temp)
+  // console.debug(`------${occupied}------------`)
+  return occupied
+}
+
+const advance = (seatMap, rules) => {
+  return seatMap.map((row, y) => {
+    return row.map((col, x) => {
+      return update({ x, y, seatMap, rules })
+    })
+  })
+}
+
+const update = ({ x, y, seatMap, rules = 'proximity' }) => {
+  let leaveThreshold = 4
+  let processor = occupiedNearby
+  if (rules === 'visibility') {
+    leaveThreshold = 5
+    processor = occupiedLineOfSite
+  }
+
+  let next = seatMap[y][x]
+  switch (seatMap[y][x]) {
+    case '.':
+      // Floor (.) never changes; seats don't move, and nobody sits on the floor.
+      next = seatMap[y][x]
+      break
+    case 'L':
+      // If a seat is empty (L) and there are no occupied seats adjacent to it, the seat becomes occupied.
+      if (processor({ x, y, seatMap }) === 0) {
+        next = '#'
+      }
+      break
+    case '#':
+      // If a seat is occupied (#) and four or more seats adjacent to it are also occupied, the seat becomes empty.
+      // We subtract 1 so we don't count the target seat
+      if (processor({ x, y, seatMap }) - 1 >= leaveThreshold) {
+        next = 'L'
+      }
+      break
+    default:
+      // Otherwise, the seat's state does not change.
+      next = seatMap[y][x]
+  }
+
+  return next
+}
+
+module.exports = {
+  format,
+  parse,
+  advance,
+  occupiedLineOfSite
+}
diff --git a/2020/day-11/seating.test.js b/2020/day-11/seating.test.js
new file mode 100644
index 0000000..8ecd693
--- /dev/null
+++ b/2020/day-11/seating.test.js
@@ -0,0 +1,227 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { format, parse, advance, occupiedLineOfSite } = require('./seating')
+
+const testData = [
+`L.LL.LL.LL
+LLLLLLL.LL
+L.L.L..L..
+LLLL.LL.LL
+L.LL.LL.LL
+L.LLLLL.LL
+..L.L.....
+LLLLLLLLLL
+L.LLLLLL.L
+L.LLLLL.LL`
+]
+testData.push(
+`#.##.##.##
+#######.##
+#.#.#..#..
+####.##.##
+#.##.##.##
+#.#####.##
+..#.#.....
+##########
+#.######.#
+#.#####.##`
+)
+testData.push(
+`#.LL.L#.##
+#LLLLLL.L#
+L.L.L..L..
+#LLL.LL.L#
+#.LL.LL.LL
+#.LLLL#.##
+..L.L.....
+#LLLLLLLL#
+#.LLLLLL.L
+#.#LLLL.##`
+)
+testData.push(
+`#.##.L#.##
+#L###LL.L#
+L.#.#..#..
+#L##.##.L#
+#.##.LL.LL
+#.###L#.##
+..#.#.....
+#L######L#
+#.LL###L.L
+#.#L###.##`
+)
+testData.push(
+`#.#L.L#.##
+#LLL#LL.L#
+L.L.L..#..
+#LLL.##.L#
+#.LL.LL.LL
+#.LL#L#.##
+..L.L.....
+#L#LLLL#L#
+#.LLLLLL.L
+#.#L#L#.##`
+)
+testData.push(
+`#.#L.L#.##
+#LLL#LL.L#
+L.#.L..#..
+#L##.##.L#
+#.#L.LL.LL
+#.#L#L#.##
+..L.L.....
+#L#L##L#L#
+#.LLLLLL.L
+#.#L#L#.##`
+)
+
+const testDataPart2 = [testData[0]]
+testDataPart2.push(
+`#.##.##.##
+#######.##
+#.#.#..#..
+####.##.##
+#.##.##.##
+#.#####.##
+..#.#.....
+##########
+#.######.#
+#.#####.##`
+)
+testDataPart2.push(
+`#.LL.LL.L#
+#LLLLLL.LL
+L.L.L..L..
+LLLL.LL.LL
+L.LL.LL.LL
+L.LLLLL.LL
+..L.L.....
+LLLLLLLLL#
+#.LLLLLL.L
+#.LLLLL.L#`
+)
+testDataPart2.push(
+`#.L#.##.L#
+#L#####.LL
+L.#.#..#..
+##L#.##.##
+#.##.#L.##
+#.#####.#L
+..#.#.....
+LLL####LL#
+#.L#####.L
+#.L####.L#`
+)
+testDataPart2.push(
+`#.L#.L#.L#
+#LLLLLL.LL
+L.L.L..#..
+##LL.LL.L#
+L.LL.LL.L#
+#.LLLLL.LL
+..L.L.....
+LLLLLLLLL#
+#.LLLLL#.L
+#.L#LL#.L#`
+)
+testDataPart2.push(
+`#.L#.L#.L#
+#LLLLLL.LL
+L.L.L..#..
+##L#.#L.L#
+L.L#.#L.L#
+#.L####.LL
+..#.#.....
+LLL###LLL#
+#.LLLLL#.L
+#.L#LL#.L#`
+)
+testDataPart2.push(
+`#.L#.L#.L#
+#LLLLLL.LL
+L.L.L..#..
+##L#.#L.L#
+L.L#.LL.L#
+#.LLLL#.LL
+..#.L.....
+LLL###LLL#
+#.LLLLL#.L
+#.L#LL#.L#`
+)
+
+describe('--- Day 11: Seating System ---', () => {
+  describe('Part 1', () => {
+    describe('advance()', () => {
+      it('advances the seating state', () => {
+        const results = testData.map((data) => {
+          return format(
+            advance(
+              parse(data)
+            )
+          )
+        })
+
+        for (let x = 1; x < testData.length; x++) {
+          console.debug('Step', x)
+          expect(results[x - 1]).to.equal(testData[x])
+        }
+        const finalOccupancy = (results[results.length - 1].match(/#/g) || []).length
+        expect(finalOccupancy).to.equal(37)
+      })
+    })
+  })
+  describe('Part 2', () => {
+    describe('occupiedLineOfSite()', () => {
+      it('counts the occupied seats visible in each direction', () => {
+        const data =
+`.......#.
+...#.....
+.#.......
+.........
+..#L....#
+....#....
+.........
+#........
+...#.....`
+        expect(occupiedLineOfSite({ x: 3, y: 4, seatMap: parse(data) })).to.equal(8)
+      })
+      it('cannot see occupied seats past an available seat', () => {
+        const data =
+`.............
+.L.L.#.#.#.#.
+.............`
+        expect(occupiedLineOfSite({ x: 1, y: 1, seatMap: parse(data) })).to.equal(0)
+      })
+      it('can look in all compass directions', () => {
+        const data =
+`.##.##.
+#.#.#.#
+##...##
+...L...
+##...##
+#.#.#.#
+.##.##.`
+        expect(occupiedLineOfSite({ x: 3, y: 3, seatMap: parse(data) })).to.equal(0)
+      })
+    })
+    describe('advance()', () => {
+      it('accepts visibility rules instead of proximity', () => {
+        const results = testDataPart2.map((data) => {
+          return format(
+            advance(
+              parse(data), 'visibility'
+            )
+          )
+        })
+
+        for (let x = 1; x < testDataPart2.length; x++) {
+          console.debug('Step', x)
+          console.debug(results[x - 1])
+          expect(results[x - 1]).to.equal(testDataPart2[x])
+        }
+        const finalOccupancy = (results[results.length - 1].match(/#/g) || []).length
+        expect(finalOccupancy).to.equal(26)
+      })
+    })
+  })
+})
diff --git a/2020/day-11/solution.js b/2020/day-11/solution.js
new file mode 100644
index 0000000..4537a8f
--- /dev/null
+++ b/2020/day-11/solution.js
@@ -0,0 +1,49 @@
+const fs = require('fs')
+const path = require('path')
+const filePath = path.join(__dirname, 'input.txt')
+const { parse, advance, format } = require('./seating')
+
+fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
+  if (err) throw err
+
+  initData = initData.trim()
+
+  const resetInput = () => {
+    // Deep copy to ensure we aren't mutating the original data
+    return JSON.parse(JSON.stringify(initData))
+  }
+
+  const part1 = () => {
+    let data = resetInput()
+    let last = 0
+    let curr = 1
+    while (curr !== last) {
+      last = curr
+      data = format(advance(parse(data)))
+      // count the current occupied seats
+      curr = (data.match(/#/g) || []).length
+    }
+    return curr
+  }
+
+  const part2 = () => {
+    let data = resetInput()
+    let last = 0
+    let curr = 1
+    while (curr !== last) {
+      last = curr
+      data = format(advance(parse(data), 'visibility'))
+      // count the current occupied seats
+      curr = (data.match(/#/g) || []).length
+    }
+    return curr
+  }
+  const answers = []
+  answers.push(part1())
+  answers.push(part2())
+
+  answers.forEach((ans, idx) => {
+    console.info(`-- Part ${idx + 1} --`)
+    console.info(`Answer: ${ans}`)
+  })
+})