day 8 p1

src/day_9.jl

@@ -0,0 +1,91 @@
+include(joinpath(readchomp(`git rev-parse --show-toplevel`), "aoc.jl"))
+import .Aoc: @aoc
+using Pipe: @pipe
+using Combinatorics
+
+
+function p1(input::Vector{String})
+	map = []
+	for l in input
+		push!(map, [ parse(Int, c) for c in l ])
+	end
+	risks = 0
+	for x in 1:length(map)
+		for y in 1:length(map[1])
+			adjacent = []
+			for (a,b) in [[0,1], [1,0], [0,-1], [-1,0]]
+				i = x + a
+				j = y + b
+
+				if i < 1 || i > length(map) || j < 1 || j > length(map[1])
+					continue
+				end
+				push!(adjacent, map[i][j])
+			end
+			@info map[x][y]
+			@info adjacent
+			if map[x][y] < minimum(adjacent)
+				@info "low"
+				risks += map[x][y] + 1
+			end
+		end
+	end
+	return risks
+end
+
+function lowpoints(map)
+	low = []
+	for x in 1:length(map)
+		for y in 1:length(map[1])
+			adjacent = []
+			for (a,b) in [[0,1], [1,0], [0,-1], [-1,0]]
+				i = x + a
+				j = y + b
+
+				if i < 1 || i > length(map) || j < 1 || j > length(map[1])
+					continue
+				end
+				push!(adjacent, map[i][j])
+			end
+			if map[x][y] < minimum(adjacent)
+				push!(low, [x,y])
+			end
+		end
+	end
+	return low
+end
+
+function search(map, pos)
+	queue = [pos]
+	visited = [pos]
+
+	while length(queue) > 0
+		c = popfirst!(queue)
+		h = map[c[1], c[2]]
+		for pos in [ [x+i,y+j] for (i,j) in zip([0,1,0,-1], [1,0,-1,0]) ]
+			if p[1] < 1 || p[1] > length(map) || p[2] < 1 || p[2] > length(map[1])
+				continue
+			end
+			if pos ∉ visited
+				h2 = map[p[1]][p[2]]
+				if h2 < 9 && h2 > h
+					push!(visited, pos)
+					push!(queue, pos)
+				end
+			end
+		end
+	end
+	return visited
+end
+
+function p2(input::Vector{String})
+	map = []
+	for l in input
+		push!(map, [ parse(Int, c) for c in l ])
+	end
+	low = lowpoints(map)
+	basin_sizes = [ length(search(map, p)) for p in low ]
+	return prod(sort(basin_sizes)[end-2:end])
+end
+
+@aoc(2021, 9)