feat: day2 part2 solution runtime down to 400ms (from 4700)HEAD2025

1 files changed, 23 insertions, 27 deletions

diff --git a/day2/part2/main.ha b/day2/part2/main.ha
index 4778240..415295d 100644
--- a/day2/part2/main.ha
+++ b/day2/part2/main.ha
@@ -1,43 +1,42 @@
+use bytes::{equal};
 use fmt;
 use io;
-use math::{ceilf64, log10f64};
 use os;
 use strconv;
-use strings::{cut, dup, freeall, fromutf8_unsafe, rtrim, split, sub};
+use strings::{cut, fromutf8_unsafe, rtrim, split, toutf8};
 
-fn digits(num: u64) u8 = {
-	return ceilf64(log10f64(num: f64)): u8;
-};
+fn u64revdigits(u: u64) ([]u8, size) = {
+	static let buf: [64]u8 = [0...];
 
-fn has_repeating_seq(num: u64) bool = {
-	let digits = digits(num);
+	let length = 0z;
+
+	for (u > 0u64) {
+		buf[length] = (u % 10): u8;
+		length += 1;
+		u /= 10;
+	};
 
-	if (digits == 1) return false;
+	return (buf, length);
+};
 
-	let divisors: []u8 = [];
-	defer free(divisors);
+fn has_repeating_seq(num: u64) bool = {
+	if (num < 11) return false;
 
-	let num_str = strconv::u64tos(num);
+	let (num_bytes, digits) = u64revdigits(num);
 
 	for (let i: u8 = 2; i <= digits; i += 1) {
 		if (digits % i == 0) {
 			let chunk_size = digits / i;
-			let first_chunk: str = "";
-			defer free(first_chunk);
+			let first_chunk: []u8 = num_bytes[..chunk_size];
 
 			let valid_seq = true;
 
-			for (let j: u8 = 0; j < i; j += 1) {
-				let chunk = dup(sub(num_str, chunk_size * j,
-					chunk_size * j + chunk_size))!;
-
-				if (j == 0) {
-					first_chunk = chunk;
-				} else {
-					if (chunk != first_chunk) {
-						valid_seq = false;
-						break;
-					};
+			for (let j: u8 = 1; j < i; j += 1) {
+				let chunk = num_bytes[chunk_size * j..chunk_size * (j + 1)];
+
+				if (!equal(chunk, first_chunk)) {
+					valid_seq = false;
+					break;
 				};
 			};
 
@@ -66,9 +65,6 @@ export fn main() void = {
 		let start = strconv::stou64(range_ends.0)!;
 		let end = strconv::stou64(range_ends.1)!;
 
-		let start_digits = digits(start);
-		let end_digits = digits(end);
-
 		for (let num = start; num <= end; num += 1) {
 			if (has_repeating_seq(num)) answer += num;
 		};