[aoc/2021] Finish day 9

Pathetic me even forgot how to implement forest fire )-;

2 files changed, 53 insertions, 0 deletions

diff --git a/aoc/2021/09/part-one.zig b/aoc/2021/09/part-one.zig
new file mode 100644
index 0000000..8e3ae15
--- /dev/null
+++ b/aoc/2021/09/part-one.zig
@@ -0,0 +1,33 @@
+const print = std.debug.print;
+const std = @import("std");
+
+const input = @embedFile("input");
+
+inline fn get(x: i8, y: i8) u8 {
+    return switch (x) {
+        0...99 => switch (y) {
+            0...99 => input[@intCast(usize, x) + @intCast(usize, y) * 101],
+            else => ':',
+        },
+        else => ':',
+    };
+}
+
+pub fn main() void {
+    var sum: usize = 0;
+    defer print("{}\n", .{ sum });
+
+    var row: i8 = 0;
+    while (row < 100) : (row += 1) {
+        var col: i8 = 0;
+        while (col < 100) : (col += 1) {
+            const height = get(col, row);
+            sum += @boolToInt(@reduce(.And, @Vector(4, u8){
+                get(col + 1, row),
+                get(col, row + 1),
+                get(col - 1, row),
+                get(col, row - 1),
+            } > @splat(4, height))) * (height - '/');
+        }
+    }
+}
diff --git a/aoc/2021/09/part-two.py b/aoc/2021/09/part-two.py
new file mode 100644
index 0000000..99524c4
--- /dev/null
+++ b/aoc/2021/09/part-two.py
@@ -0,0 +1,20 @@
+from collections import deque
+from functools import reduce
+from operator import mul
+from sys import stdin
+
+heightmap = [[int(c) for c in s] for s in stdin.read().strip().split()]
+get = lambda y, x: 10 if min(x, y) < 0 or max(x, y) > 99 else heightmap[y][x]
+adjacent = lambda y, x: ((y, x + 1), (y + 1, x), (y, x - 1), (y - 1, x))
+basins = {(i, j): 0 for i, row in enumerate(heightmap)
+          for j, height in enumerate(row)
+          if all(height < get(y, x) for y, x in adjacent(i, j))}
+queue, visited = deque((key, key) for key in basins), set()
+while queue:
+    key, pos = queue.popleft()
+    if pos in visited: continue
+    basins[key] += 1
+    visited.add(pos)
+    for adj in adjacent(*pos):
+        if get(*adj) < 9 and adj not in visited: queue.append((key, adj))
+print(reduce(mul, sorted(basins.values(), reverse=True)[:3]))