day 13: rust

13/README.md

@@ -0,0 +1,22 @@
+# [Day 13](https://adventofcode.com/2023/day/13) 
+:gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift:
+
+Today's language: **Rust**
+
+Lines of code: **84**
+
+Execution time: **0,002 s**
+
+Once again, binary encoding is used to transform every line and every column of each pattern into one unsigned int.
+The columns and lines are stored in one vector each. This means the same function can be used to find the reflection axis for both.
+
+For task 2, we don't check whether two lines are equal, but whether they differ by 0 or 1 bit.
+
+This approach is super fast since it has 0 heap allocations in loops and comparing two ints is way faster than comparing two strings.
+
+```shell
+rustc day13.rs
+./day13RUN
+```
+
+<!-- binary encoding ftw -->

13/day13.rs

@@ -0,0 +1,94 @@
+use std::io::{self, BufRead};
+
+
+fn get_diff_bits_count(a: u32, b: u32) -> usize {  // return 0 if equal, 1 if 1 bit is different, else 2
+    let diff = a ^ b;
+    if diff == 0 { return 0 }
+    if (diff & diff.overflowing_sub(1).0) == 0 { return 1 }
+    return 2;
+}
+
+fn find_reflection_axis(pattern: &Vec<u32>, has_smack: bool) -> Option<usize> {
+    for i in 1..pattern.len() {
+        let mut found_smack = false;
+        let diff = get_diff_bits_count(pattern[i-1], pattern[i]);
+        if has_smack && diff == 1 {
+            found_smack = true;
+        }
+        if diff == 0 || found_smack {  // find two identical neighbors (or differing by 1 for task 2
+            let mut matching = true;
+            for j in 1..i.min(pattern.len() - i) {  // check top and bottom if equal (or diff by 1 bit if has_smack)
+                let diff = get_diff_bits_count(pattern[i-1-j], pattern[i+j]);
+                if diff == 0 { continue; }
+                if has_smack && diff == 1 && !found_smack {  // allow only one smack
+                    found_smack = true;
+                    continue;
+                }
+                matching = false; 
+                break;
+            }
+            if matching && (!has_smack || (has_smack && found_smack)) {  // require smack for task 2
+                return Some(i);
+            }
+        }
+    }
+    return None;
+}
+
+fn do_task(horizontal: &Vec<u32>, vertical: &Vec<u32>, has_smack: bool) -> usize {
+    let mut mirror_sum: usize = 0;
+    if let Some(x) = find_reflection_axis(&horizontal, has_smack) {
+        mirror_sum += x * 100;
+    }
+    if let Some(x) = find_reflection_axis(&vertical, has_smack) {
+        mirror_sum += x;
+    }
+    return mirror_sum;
+}
+
+
+
+fn main() {
+    // let input = "example.txt";
+    let input = "input.txt";
+    let lines = read_lines(&input);
+    let mut horizontal: Vec<u32> = Vec::new();
+    let mut vertical: Vec<u32> = Vec::new();
+    horizontal.reserve(20);
+    vertical.reserve(20);
+    let mut mirror_sum1: usize = 0;
+    let mut mirror_sum2: usize = 0;
+    let convert = |c| -> u32 { if c == '#' { 1 } else { 0 } };
+    for line in lines.map(|r| r.ok().unwrap()) {
+        if line.len() == 0 {
+            if horizontal.len() != 0 {  // skip first time
+                mirror_sum1 += do_task(&horizontal, &vertical, false);
+                mirror_sum2 += do_task(&horizontal, &vertical, true);
+            }
+            horizontal.clear();
+            vertical.clear();
+            continue;
+        }
+        if horizontal.len() == 0 {  // 0 for each column
+            (0..line.len()).for_each(|_| vertical.push(0));
+        }
+        horizontal.push(0);
+        for (i, n) in line.chars().map(|c| convert(c)).enumerate() {
+            *horizontal.last_mut().unwrap() |= (n << i);
+            vertical[i] |= (n << (horizontal.len()-1));
+        }
+    }
+    mirror_sum1 += do_task(&horizontal, &vertical, false);
+    mirror_sum2 += do_task(&horizontal, &vertical, true);
+    println!("Sum: (1): {}", mirror_sum1);
+    println!("Sum: (2): {}", mirror_sum2);
+}
+
+fn read_lines<P>(filename: P) -> io::Lines<io::BufReader<std::fs::File>>
+where P: AsRef<std::path::Path>, {
+    return match std::fs::File::open(filename) {
+        Err(why) => panic!("Could not open file. {}", why),
+        Ok(file) => std::io::BufReader::new(file).lines()
+    };
+}
+

README.md

@@ -13,5 +13,8 @@ This is a repository for my solutions for the [advent of code 2023](https://adve
 | [07](07) | Rust     | 210           | 0,007 s         | not pretty, but pretty fast   |
 | [08](08) | Rust     | 101           | 0,039 s         |                               |
 | [09](09) | Rust     | 88            | 0,003 s         | implemented triangle datatype |
+| [10](10) | Rust     | 136           | 0,003 s         | lots of bitwise operations    |
+| [11](11) | Rust     | 66            | 0,005 s         |                               |
+| [13](13) | Rust     | 84            | 0,002 s         | binary encoding ftw           |
 
  Lines of code are without blank lines and comments