72 lines
2.3 KiB
Zig
72 lines
2.3 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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var allocator: std.mem.Allocator = undefined;
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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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allocator = arena.allocator();
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try std.testing.expectEqual(try solve(example, 10), 26);
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const result = try solve(input, 2000000);
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try std.io.getStdOut().writer().print("{}\n", .{result});
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}
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const Interval = struct {
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l: i64,
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r: i64,
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};
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fn lesserThan(context: void, a: *Interval, b: *Interval) bool {
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_ = context;
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return a.l < b.l;
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}
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fn solve(puzzle: []const u8, yline: i64) !i64 {
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var it = std.mem.tokenize(u8, puzzle, "\n");
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var intervals = std.ArrayList(*Interval).init(allocator);
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// process input
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while (it.next()) |line| {
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var coords = std.mem.tokenize(u8, line, "Sensor at x=, y=: closest beacon is at x=, y=");
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const sx = try std.fmt.parseInt(i64, coords.next() orelse continue, 10);
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const sy = try std.fmt.parseInt(i64, coords.next() orelse unreachable, 10);
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const bx = try std.fmt.parseInt(i64, coords.next() orelse unreachable, 10);
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const by = try std.fmt.parseInt(i64, coords.next() orelse unreachable, 10);
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const d = try std.math.absInt(sx - bx) + try std.math.absInt(sy - by);
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if (sy - d > yline or sy + d < yline) {
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continue;
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}
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const l = d - try std.math.absInt(yline - sy);
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var i = try allocator.create(Interval);
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i.* = Interval{ .l = sx - l, .r = sx + l };
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try intervals.append(i);
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}
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// sort by left bound
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std.sort.sort(*Interval, intervals.items, {}, lesserThan);
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// Reduce intervals and compute results
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var n: i64 = 0;
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var i: usize = 0;
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while (i < intervals.items.len) : (i += 1) {
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var int = intervals.items[i];
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var j = i + 1;
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while (j < intervals.items.len) {
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const jnt = intervals.items[j];
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if (jnt.l <= int.r) { // jint overlaps
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if (jnt.r > int.r) {
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int.r = jnt.r;
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}
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_ = intervals.orderedRemove(j);
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continue;
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} else {
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break;
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}
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j += 1;
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}
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n = n + int.r - int.l;
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}
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return n;
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}
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