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const std = @import("std");
const aoc = @import("aoc");
const preamble_size = 25;
fn preambleHasSum(preamble: []u64, target: u64) bool {
for (preamble) |v1| {
for (preamble) |v2| {
if (v1 != v2 and v1 + v2 == target)
return true;
}
}
return false;
}
fn getInvalid(allocator: std.mem.Allocator, input: []u8) !u64 {
var preamble = std.ArrayList(u64).init(allocator);
defer preamble.deinit();
var i: u64 = 0;
var numit = std.mem.tokenize(u8, input, "\n");
while (numit.next()) |numstr| : (i += 1) {
const num = try std.fmt.parseInt(u64, numstr, 10);
if (i > preamble_size) {
if (!preambleHasSum(preamble.items, num)) {
return num;
}
preamble.items[(i - 1) % preamble_size] = num;
} else {
try preamble.append(num);
}
}
return aoc.Error.InvalidInput;
}
fn listSum(items: []u64) u64 {
var sum: u64 = 0;
for (items) |i|
sum += i;
return sum;
}
fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
const answer = try getInvalid(allocator, input);
return try std.fmt.allocPrint(allocator, "{d}", .{answer});
}
fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
const invalid = try getInvalid(allocator, input);
var numset = std.ArrayList(u64).init(allocator);
defer numset.deinit();
var numit = std.mem.tokenize(u8, input, "\n");
while (true) {
const sum = listSum(numset.items);
if (sum < invalid) {
const numstr = numit.next();
if (numstr == null) break;
const num = try std.fmt.parseInt(u64, numstr.?, 10);
try numset.append(num);
} else if (sum > invalid) {
_ = numset.orderedRemove(0);
} else {
break;
}
}
if (numset.items.len > 0) {
const answer = std.mem.min(u64, numset.items) + std.mem.max(u64, numset.items);
return try std.fmt.allocPrint(allocator, "{d}", .{answer});
}
return null;
}
pub const main = aoc.main(part1, part2, .{ "466456641", "55732936" });
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