day9 p1

day9/day9.jl

@@ -0,0 +1,101 @@
+#!/usr/bin/env julia
+
+using Test
+
+struct Move
+  direction :: Char
+  count :: Int
+end
+
+mutable struct State
+  head_x :: Int
+  head_y :: Int
+  tail_x :: Int
+  tail_y :: Int
+end
+
+function parse_move(line)
+  parts = split(line, limit=2)
+  return Move(parts[1][1], parse(Int, parts[2]))
+end
+
+function read_moves(io)
+  return [parse_move(line) for line in readlines(io)]
+end
+
+function apply_move(state, direction)
+  if direction == 'U'
+    state.head_y += 1
+  elseif direction == 'D'
+    state.head_y -= 1
+  elseif direction == 'L'
+    state.head_x -= 1
+  elseif direction == 'R'
+    state.head_x += 1
+  end
+  x_diff = state.head_x - state.tail_x
+  y_diff = state.head_y - state.tail_y
+  if abs(x_diff) <= 1 && abs(y_diff) <= 1
+    return state
+  end
+  if abs(x_diff) <= 1
+    state.tail_x += x_diff
+    state.tail_y += sign(y_diff) * (abs(y_diff) - 1)
+  elseif abs(y_diff) <= 1
+    state.tail_y += y_diff
+    state.tail_x += sign(x_diff) * (abs(x_diff) - 1)
+  else
+    throw(DomainError("invalid state"))
+  end 
+  return state
+end
+
+function get_visited(moves)
+  visited = Set{NTuple{2, Int}}()
+  state = State(0, 0, 0, 0)
+  push!(visited, (state.tail_x, state.tail_y))
+  for move in moves
+    for _ in 1:move.count
+      state = apply_move(state, move.direction)
+      push!(visited, (state.tail_x, state.tail_y))
+    end
+  end
+  return visited
+end
+
+function visited_map(visited)
+  (min_x, max_x) = extrema([t[1] for t in visited])
+  (min_y, max_y) = extrema([t[2] for t in visited])
+  nrows = max_y - min_y + 1
+  ncols = max_x - min_x + 1
+  vmap = zeros(Int, nrows, ncols)
+  for (x, y) in visited
+    vmap[nrows - (y - min_y), (x - min_x + 1)] = 1
+  end
+  return vmap
+end
+
+function test()
+  @testset "visited count" verbose=true begin
+    @test length(get_visited(read_moves("example.txt"))) == 13
+    @test length(get_visited(read_moves("input.txt"))) == 6037
+  end
+end
+
+function main()
+  if size(ARGS, 1) == 0
+    test()
+  else
+    infile = ARGS[1]
+    println("infile = ", infile)
+    moves = read_moves(infile)
+    println("moves: ", moves)
+    visited = get_visited(moves)
+    println("visited: ", visited)
+    println("count  : ", length(visited))
+    display(visited_map(visited))
+    println()
+  end
+end
+
+main()

day9/example.txt

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+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2