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