julia day10 (#55)

* [Julia] Day 10 based on @carstenbauer's solution

inputs/10_example.txt

@@ -0,0 +1,5 @@
+..F7.
+.FJ|.
+SJ.L7
+|F--J
+LJ...

inputs/10_example2.txt

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+FF7FSF7F7F7F7F7F---7
+L|LJ||||||||||||F--J
+FL-7LJLJ||||||LJL-77
+F--JF--7||LJLJ7F7FJ-
+L---JF-JLJ.||-FJLJJ7
+|F|F-JF---7F7-L7L|7|
+|FFJF7L7F-JF7|JL---7
+7-L-JL7||F7|L7F-7F7|
+L.L7LFJ|||||FJL7||LJ
+L7JLJL-JLJLJL--JLJ.L

solutions/10_moelf.txt

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+6890
+453

src/julia/10_moelf.jl

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+const CI = CartesianIndex{2}
+
+# Matrix coord:    up         down      right     left
+const U, D, R, L = CI(-1, 0), CI(1, 0), CI(0, 1), CI(0, -1)
+const FOUR_DIRS = (U, D, L, R)
+
+const CONNECTIONS = Dict(
+    '|' => (U, D),
+    '-' => (L, R),
+    'L' => (U, R),
+    'J' => (U, L),
+    '7' => (L, D),
+    'F' => (R, D),
+)
+
+function in_out(pipe, in_dir)
+    E1, E2 = CONNECTIONS[pipe]
+    if in_dir == E1
+        E2
+    elseif in_dir == E2
+        E1
+    else
+        nothing
+    end
+end
+
+function step(M, here, here_dir)
+    next = here + here_dir
+    next_pipe = M[next]
+    if next_pipe == 'S'
+        return next, next
+    end
+    next_dir = in_out(next_pipe, -here_dir)
+    return next, next_dir
+end
+
+function impl1(M, pos, dir)
+    res = 0
+    loop_pipes = [pos]
+    while true
+        pos, dir = step(M, pos, dir)
+        push!(loop_pipes, pos)
+        res += 1
+        M[pos] == 'S' && break
+    end
+    return res ÷ 2, loop_pipes
+end
+
+function main(path)
+    M = stack(readlines(path); dims=1)
+    pos = findfirst(==('S'), M)::CI
+    dir_idx = findall(FOUR_DIRS) do dir
+        !isassigned(M, pos + dir) && return false
+        sym = M[pos+dir]
+        !haskey(CONNECTIONS, sym) && return false
+        out_dir = in_out(sym, -dir)
+        !isnothing(out_dir)
+    end
+    dirs = FOUR_DIRS[dir_idx]
+    p1, main_loop_pipes = impl1(M, pos, dirs[begin])
+    println(p1)
+
+    # replace 'S' with real pipe
+    M[pos] = findfirst(CONNECTIONS) do v
+        Set(Tuple(v)) == Set(Tuple(dirs))
+    end
+    # clear out non-pipe map with ' '
+    for c in CartesianIndices(M)
+        if c ∉ main_loop_pipes
+            M[c] = ' '
+        end
+    end
+
+    for col in eachcol(M)
+        inside = false
+        path_start = area_start = 0
+        if first(col) != ' '
+            path_start = 1
+        else
+            area_start = 1
+        end
+        for (i, c) in enumerate(col)
+            # maintain state
+            c in (' ', '|') && continue
+
+            prevc = get(col, i - 1, '.')
+            if prevc == ' ' # area -> path
+                col[area_start:i-1] .= inside ? 'I' : 'O'
+                area_start = nothing
+                path_start = i
+            end
+
+            nextc = get(col, i + 1, '.')
+            if nextc == ' ' # path -> area
+                if string(col[path_start], c) ∉ ("FL", "7J")
+                    inside = !inside
+                end
+                area_start = i + 1
+                path_start = nothing
+            elseif c in ('L', 'J', '-') # path -> new path
+                if string(col[path_start], c) ∉ ("FL", "7J")
+                    inside = !inside
+                end
+                path_start = i + 1
+            end
+        end
+    end
+    println(count(==('I'), M))
+
+end
+
+(abspath(PROGRAM_FILE) == @__FILE__) && (main(ARGS[1]))