[Day 06] Add solutions

day06.lua

@@ -1,35 +1,184 @@
 local read_input = require('lib.read_input')
+local str = require('lib.split_str')
+local copy = require('lib.copy')
 
 local Day06 = {}
 
-function Day06:new(o)
+function Day06:new(o, input)
     o = o or {}
 
     o.parent = self
     setmetatable(o, self)
     self.__index = self
 
+    o.initial_state = (input and input.input) or {}
+    o.input = copy(o.initial_state)
     return o
 end
 
+local NORTH = {
+    x = -1,
+    y = 0
+}
+local EAST = {
+    x = 0,
+    y = 1
+}
+local SOUTH = {
+    x = 1,
+    y = 0
+}
+local WEST = {
+    x = 0,
+    y = -1
+}
+
+function Day06:turn_guard()
+    local guard = self.input.guard
+
+    if guard.direction.x == NORTH.x and guard.direction.y == NORTH.y then
+        guard.direction = EAST
+    elseif guard.direction.x == EAST.x and guard.direction.y == EAST.y then
+        guard.direction = SOUTH
+    elseif guard.direction.x == SOUTH.x and guard.direction.y == SOUTH.y then
+        guard.direction = WEST
+    elseif guard.direction.x == WEST.x and guard.direction.y == WEST.y then
+        guard.direction = NORTH
+    end
+end
+
+
+function Day06:move_guard()
+    local guard = self.input.guard
+    local obstacles = self.input.obstacles
+
+    for _ = 1, 4 do
+        local x = guard.x + guard.direction.x
+        local y = guard.y + guard.direction.y
+
+        if obstacles[x] and obstacles[x][y] then
+            self:turn_guard()
+        else
+            guard.x = x
+            guard.y = y
+            return
+        end
+    end
+    print("Guard is boxed in and cannot move!")
+end
+
+function Day06:out_of_bounds()
+    local g = self.input.guard
+    local d = self.input.dimensions
+
+    return g.x < 1 or d.height < g.x
+    or g.y < 1 or d.width < g.y
+end
+
+function Day06:state_visited(res)
+    local g = self.input.guard
+    local gs = res.guard_states
+
+    return gs[g.x] and gs[g.x][g.y]
+        and gs[g.x][g.y][g.direction.x]
+        and gs[g.x][g.y][g.direction.x][g.direction.y]
+end
+
+function Day06:visit_state(res)
+    local g = self.input.guard
+    local gs = res.guard_states
+
+    gs[g.x] = gs[g.x] or {}
+    gs[g.x][g.y] = gs[g.x][g.y] or {}
+    gs[g.x][g.y][g.direction.x] = gs[g.x][g.y][g.direction.x] or {}
+    gs[g.x][g.y][g.direction.x][g.direction.y] = true
+end
+
+function Day06:position_visited(res)
+    local guard = self.input.guard
+    local pos = res.positions
+    return pos[guard.x] and pos[guard.x][guard.y]
+end
+
+function Day06:visit_position(res)
+    local guard = self.input.guard
+    local pos = res.positions
+    pos[guard.x] = pos[guard.x] or {}
+    pos[guard.x][guard.y] = true
+end
+
+function Day06:simulate_guard()
+    local res = {
+        count = 0,
+        positions = {},
+        guard_states = {},
+        is_loop = false
+    }
+
+    while not self:out_of_bounds() do
+        if self:state_visited(res) then
+            res.is_loop = true
+            return res
+        end
+        self:visit_state(res)
+
+        if not self:position_visited(res) then
+            res.count = res.count + 1
+        end
+        self:visit_position(res)
+        self:move_guard()
+    end
+
+    return res
+end
+
 local Part1 = Day06:new()
 
 function Part1:new(input)
     local o = {}
-    Day06.new(self, o)
+    Day06.new(self, o, input)
 
     return o
 end
 
+function Part1:solve()
+    return self:simulate_guard().count
+end
+
 local Part2 = Day06:new()
 
 function Part2:new(input)
     local o = {}
-    Day06.new(self, o)
+    Day06.new(self, o, input)
 
     return o
 end
 
+function Part2:set_obstacle(x, y, value)
+    self.input.obstacles[x] = self.input.obstacles[x] or {}
+    self.input.obstacles[x][y] = value
+end
+
+function Part2:solve()
+    local guard = copy(self.input.guard)
+    local obstacle_candidates = self:simulate_guard().positions
+
+    local loops_found = 0
+    for x, ys in pairs(obstacle_candidates) do
+        for y, _ in pairs(ys) do
+            if x ~= guard.x or y ~= guard.y then
+                self.input.guard = copy(guard)
+                self:set_obstacle(x, y, true)
+                if self:simulate_guard().is_loop then
+                    loops_found = loops_found + 1
+                end
+                self:set_obstacle(x, y, nil)
+            end
+        end
+    end
+    return loops_found
+end
+
 local Input = {}
 
 function Input:new(o)
@@ -39,15 +188,54 @@ function Input:new(o)
     setmetatable(o, self)
     self.__index = self
 
-    local input = read_input("example input here")
-
+    local input = read_input("....#.....\
+.........#\
+..........\
+..#.......\
+.......#..\
+..........\
+.#..^.....\
+........#.\
+#.........\
+......#...")
+
+    local lines = str.split(input, "\n")
+
+    local state = {
+        guard = {},
+        obstacles = {},
+        dimensions = {
+            width = #lines[1],
+            height = #lines
+        }
+    }
+    local obstacle = "#"
+    local guard = "^"
+    for x, line in pairs(lines) do
+        for y = 1, #line do
+            if line:byte(y) == obstacle:byte(1) then
+                state.obstacles[x] = state.obstacles[x] or {}
+                state.obstacles[x][y] = true
+            elseif line:byte(y) == guard:byte(1) then
+                state.guard = {
+                    direction = NORTH,
+                    x = x,
+                    y = y
+                }
+            end
+        end
+    end
+
+    o.input = state
     return o
 end
 
 local input = Input:new()
 
+-- Part 1: 5095
 local p1 = Part1:new(input)
 print("Part 1: " .. p1:solve())
 
---local p2 = Part2:new(input)
---print("Part 2: " .. p2:solve())
+-- 1933
+local p2 = Part2:new(input)
+print("Part 2: " .. p2:solve())

lib/copy.lua

@@ -0,0 +1,9 @@
+-- https://gist.github.com/tylerneylon/81333721109155b2d244
+local function copy(obj)
+    if type(obj) ~= 'table' then return obj end
+    local res = {}
+    for k, v in pairs(obj) do res[copy(k)] = copy(v) end
+    return res
+end
+
+return copy