95 lines
3.1 KiB
Zig
95 lines
3.1 KiB
Zig
const std = @import("std");
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pub fn main() !void {
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var allocator = std.heap.GeneralPurposeAllocator(.{}){};
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var f = std.fs.File { .handle = try std.os.open("input-part1", std.os.O_RDONLY, 0) };
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var buffer : [1024]u8 = undefined;
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var expenses = std.ArrayList(u32).init(&allocator.allocator);
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defer expenses.deinit();
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var byte_buffer = std.ArrayList(u8).init(&allocator.allocator);
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defer byte_buffer.deinit();
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var read = try f.read(&buffer);
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std.log.info("Read {} bytes", .{read});
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while (read != 0) {
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for (buffer) | v, k | {
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if (std.ascii.isDigit(v)) {
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try byte_buffer.append(v);
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}
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if (v == '\n') {
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var x = atoi(byte_buffer.items[0..]);
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//std.log.debug("{}", .{x});
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try expenses.append(x);
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// Set the position back to zero, without freeing existing memory
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byte_buffer.deinit();
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byte_buffer = std.ArrayList(u8).init(&allocator.allocator);
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}
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}
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read = try f.read(&buffer);
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//std.log.info("Read {} bytes", .{read});
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}
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//std.log.info("{}", .{expenses.items.len});
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part1(expenses.items[0..]);
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part2(expenses.items[0..]);
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}
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fn part2(expenses : []u32) void {
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var i : u32 = 0;
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var elements : [3]u32 = undefined;
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while (i < expenses.len) : (i += 1) {
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var j : u32 = 0;
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while (j < expenses.len) : (j += 1) {
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var k : u32 = 0;
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while (k < expenses.len) : (k += 1) {
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if (k == j or k == 1) {
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continue;
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}
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if (expenses[i] + expenses[j] + expenses[k] == 2020) {
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elements[0] = expenses[i];
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elements[1] = expenses[j];
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elements[2] = expenses[k];
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}
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}
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}
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}
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std.log.info("{} and {} and {} sum to {} and multiply to {}",
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.{elements[0], elements[1], elements[2], elements[0] + elements[1] + elements[2],
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elements[0] * elements[1] * elements[2]});
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}
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fn part1(expenses : []u32) void {
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var i : u32 = 0;
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var elements : [2]u32 = undefined;
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while (i < expenses.len) : (i += 1) {
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var j : u32 = 0;
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while (j < expenses.len) : (j += 1) {
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if (i == j) {
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continue;
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}
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if (expenses[i] + expenses[j] == 2020) {
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elements[0] = expenses[i];
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elements[1] = expenses[j];
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}
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}
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}
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std.log.info("{} and {} sum to {} and multiply to {}",
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.{elements[0], elements[1], elements[0] + elements[1],
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elements[0] * elements[1]});
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}
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fn atoi(a: []u8) u32 {
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var i : u32 = 0;
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for(a) |v, k| {
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if (! std.ascii.isDigit(v)) {
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std.log.warn("Byte {x} is not a digit", .{v});
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continue;
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}
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// 48 is '0' in ascii
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std.debug.assert(v >= 48 and v < 58);
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i += @as(u32, (v - 48) * std.math.pow(u32, 10, @intCast(u32, a.len - k - 1)));
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}
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//std.log.debug("{x} --> {}", .{a, i});
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return i;
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}
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