94 lines
2.2 KiB
Zig
94 lines
2.2 KiB
Zig
const std = @import("std");
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const aoc = @import("aoc.zig");
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const Allocator = std.mem.Allocator;
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const ArrayList = std.ArrayList;
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pub fn main() !void {
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var gpa: std.heap.GeneralPurposeAllocator(.{}) = .{};
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defer _ = gpa.deinit();
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const allocator = gpa.allocator();
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const file = try std.fs.cwd().openFile("input/day03.txt", .{});
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defer file.close();
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const text = try file.readToEndAlloc(allocator, comptime 1 << 30);
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defer allocator.free(text);
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const stdout_file = std.io.getStdOut().writer();
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var bw = std.io.bufferedWriter(stdout_file);
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const stdout = bw.writer();
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try stdout.print("{d}\n", .{part1(text)});
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try bw.flush();
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}
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const Mul = struct {
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a: u32,
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b: u32,
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};
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const MulIterator = struct {
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text: []u8,
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pos: usize,
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fn new(text: []u8) MulIterator {
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return .{
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.text = text,
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.pos = 0,
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};
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}
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fn next(self: *MulIterator) ?Mul {
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while (self.pos < self.text.len) {
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self.pos += std.mem.indexOf(u8, self.text[self.pos..], "mul(") orelse return null;
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self.pos += consume(self.text[self.pos..], "mul(").?;
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const a = parsePrefixInt(self.text[self.pos..]) orelse continue;
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self.pos += a.chars;
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self.pos += consume(self.text[self.pos..], ",") orelse continue;
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const b = parsePrefixInt(self.text[self.pos..]) orelse continue;
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self.pos += b.chars;
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self.pos += consume(self.text[self.pos..], ")") orelse continue;
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return .{ .a = a.value, .b = b.value };
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}
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return null;
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}
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};
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fn consume(text: []const u8, want: []const u8) ?usize {
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if (std.mem.startsWith(u8, text, want)) {
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return want.len;
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}
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return null;
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}
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fn parsePrefixInt(s: []u8) ?struct { value: u32, chars: usize } {
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var idx: usize = 0;
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var value: u32 = 0;
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while (idx < s.len and std.ascii.isDigit(s[idx])) {
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value *= 10;
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value += s[idx] - '0';
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idx += 1;
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}
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if (idx > 0) {
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return .{ .value = value, .chars = idx };
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}
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return null;
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}
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fn part1(text: []u8) u32 {
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var it = MulIterator.new(text);
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var sum: u32 = 0;
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while (it.next()) |mul| {
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sum += mul.a * mul.b;
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}
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return sum;
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}
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