From f1cb8ad58a58bcceb8afe1ce211828117e01c07e Mon Sep 17 00:00:00 2001
From: Julien Dessaux
Date: Thu, 8 Dec 2022 11:56:34 +0100
Subject: 2022-08 in zig

---
 2022/08-treetop-tree-house/first.zig | 106 +++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 2022/08-treetop-tree-house/first.zig

(limited to '2022/08-treetop-tree-house/first.zig')

diff --git a/2022/08-treetop-tree-house/first.zig b/2022/08-treetop-tree-house/first.zig
new file mode 100644
index 0000000..07db936
--- /dev/null
+++ b/2022/08-treetop-tree-house/first.zig
@@ -0,0 +1,106 @@
+const std = @import("std");
+
+const example = @embedFile("example");
+const input = @embedFile("input");
+
+pub fn main() anyerror!void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    try std.testing.expectEqual(try solve(example, allocator), 21);
+    const result = try solve(input, allocator);
+    try std.io.getStdOut().writer().print("{}\n", .{result});
+}
+
+fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
+    var it = std.mem.tokenize(u8, puzzle, "\n");
+    var heights = std.ArrayList(std.ArrayList(u8)).init(allocator);
+    var visibility = std.ArrayList(std.ArrayList(bool)).init(allocator);
+    // process input
+    var line = it.next() orelse unreachable;
+    const width = line.len;
+    while (true) {
+        var h = try heights.addOne();
+        var v = try visibility.addOne();
+        h.* = try std.ArrayList(u8).initCapacity(allocator, width);
+        v.* = try std.ArrayList(bool).initCapacity(allocator, width);
+        try h.*.writer().writeAll(line);
+        v.*.appendAssumeCapacity(true);
+        var i: usize = 1;
+        while (i < width - 1) : (i += 1) {
+            v.*.appendAssumeCapacity(false);
+        }
+        v.*.appendAssumeCapacity(true);
+        if (it.next()) |l| {
+            line = l;
+        } else {
+            break;
+        }
+    }
+    const lastX = width - 1;
+    const lastY = heights.items.len - 1;
+    // init first and last lines edges
+    var x: usize = 1;
+    while (x < width - 1) : (x += 1) {
+        visibility.items[0].items[x] = true;
+        visibility.items[lastY].items[x] = true;
+    }
+    // calculate visible trees in lines
+    var y: usize = 1;
+    while (y < lastY) : (y += 1) {
+        const treeline = heights.items[y];
+        // look right
+        var max = treeline.items[0];
+        x = 1;
+        while (x < lastX) : (x += 1) {
+            if (treeline.items[x] > max) {
+                visibility.items[y].items[x] = true;
+                max = treeline.items[x];
+            }
+        }
+        // look left
+        max = treeline.items[lastX];
+        x = lastX - 1;
+        while (x > 0) : (x -= 1) {
+            if (treeline.items[x] > max) {
+                visibility.items[y].items[x] = true;
+                max = treeline.items[x];
+            }
+        }
+    }
+    // calculate visible trees in columns
+    x = 1;
+    while (x < lastX) : (x += 1) {
+        // look down
+        var max = heights.items[0].items[x];
+        y = 1;
+        while (y < lastY) : (y += 1) {
+            if (heights.items[y].items[x] > max) {
+                visibility.items[y].items[x] = true;
+                max = heights.items[y].items[x];
+            }
+        }
+        // look up
+        max = heights.items[lastY].items[x];
+        y = lastY - 1;
+        while (y > 0) : (y -= 1) {
+            if (heights.items[y].items[x] > max) {
+                visibility.items[y].items[x] = true;
+                max = heights.items[y].items[x];
+            }
+        }
+    }
+    // calculate total
+    var tot: usize = 0;
+    y = 0;
+    while (y <= lastY) : (y += 1) {
+        x = 0;
+        while (x <= lastX) : (x += 1) {
+            if (visibility.items[y].items[x]) {
+                tot += 1;
+            }
+        }
+    }
+    return tot;
+}
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