102 lines
3 KiB
Zig
102 lines
3 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), 8);
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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 scenic = std.ArrayList(std.ArrayList(u64)).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 scenic.addOne();
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h.* = try std.ArrayList(u8).initCapacity(allocator, width);
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v.* = try std.ArrayList(u64).initCapacity(allocator, width);
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try h.*.writer().writeAll(line);
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var i: usize = 0;
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while (i < width) : (i += 1) {
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v.*.appendAssumeCapacity(0);
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}
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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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scenic.items[0].items[x] = 0;
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scenic.items[lastY].items[x] = 0;
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}
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// calculate scenic scores tree by tree
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var tot: usize = 0;
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var y: usize = 1;
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while (y < lastY) : (y += 1) {
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x = 1;
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while (x < lastX) : (x += 1) {
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const max = heights.items[y].items[x];
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// look right
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var sr: usize = 1; // scenic score to the right
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var i: usize = x + 1;
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while (i < lastX) : (i += 1) {
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if (heights.items[y].items[i] < max) {
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sr += 1;
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} else {
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break;
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}
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}
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// look left
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var sl: usize = 1;
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i = x - 1;
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while (i > 0) : (i -= 1) {
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if (heights.items[y].items[i] < max) {
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sl += 1;
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} else {
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break;
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}
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}
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// look down
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var sd: usize = 1;
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i = y + 1;
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while (i < lastY) : (i += 1) {
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if (heights.items[i].items[x] < max) {
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sd += 1;
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} else {
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break;
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}
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}
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// look up
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var su: usize = 1;
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i = y - 1;
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while (i > 0) : (i -= 1) {
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if (heights.items[i].items[x] < max) {
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su += 1;
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} else {
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break;
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}
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}
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const score = sr * sl * sd * su;
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if (score > tot) {
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tot = score;
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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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