day14: rust

14/README.md

@@ -0,0 +1,22 @@
+# [Day 14](https://adventofcode.com/2023/day/14) 
+:gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift::gift:
+
+Today's language: **Rust**
+
+Lines of code: **84**
+
+Execution time: **0,171 s**
+
+This solution uses a single function for the tilting procedure.
+Different tilting directions are achieved by "remapping" `x` and `y` through captures.
+
+For task 2, a cycle is searched by comparing the rocks after each nwse-tilt with all previous results. 
+After finding two equal states, only `(1.000.000.000 - cycle_start) % cycle_length` cycles have to be performed to get the correct result.
+This approach requires making copies of the 2D array in a loop, which involves expensive heap allocations.
+It is still pretty fast.
+
+```shell
+rustc day14.rs
+./day14
+```
+<!-- no bruteforce in < 90 lines -->

14/day14.rs

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+use std::io::{self, BufRead};
+
+type Rocks = Vec<Vec<u8>>;
+
+// tilt so that all 'O' characters want to DECREMENT their Y index
+// using custom `at` function that "remaps" x and y, this function can be used for all directions
+fn tilt<F>(rocks: &mut Rocks, at: F, x_len: usize, y_len: usize) 
+where F: Fn(&mut Rocks, usize, usize) -> &mut u8 {
+    for x in 0..x_len {
+        let mut next_y: usize = 0;  // lowest reachable position
+        for y in 0..y_len {
+            match *at(rocks, x, y) as char {
+                '#' => next_y = y + 1,
+                'O' => {
+                    if next_y != y {
+                        *at(rocks, x, next_y) = 'O' as u8;
+                        *at(rocks, x, y) = '.' as u8;
+                    }
+                    while next_y < y_len - 1 {
+                        next_y += 1;
+                        if *at(rocks, x, next_y) != '#' as u8 { break }
+                    }
+                },
+                _ => {},
+            }
+        }
+    }
+}
+
+//   --> y
+// |
+// V
+// x
+// West is the orientation that looks like the input
+// When printing with one of these, the rocks want to roll to the left side
+fn west_at(rocks: &mut Rocks, x: usize, y: usize) -> &mut u8 { &mut rocks[x][y] }
+fn east_at(rocks: &mut Rocks, x: usize, y: usize) -> &mut u8 { let ylen = rocks[0].len(); &mut rocks[x][ylen - y - 1] }
+fn south_at (rocks: &mut Rocks, x: usize, y: usize) -> &mut u8 { let xlen = rocks.len(); let ylen = rocks[0].len(); &mut rocks[xlen - y - 1][ylen - x - 1] }
+fn north_at (rocks: &mut Rocks, x: usize, y: usize) -> &mut u8 { let ylen = rocks[0].len(); &mut rocks[y][ylen - x - 1] }
+
+fn print<F>(rocks: &mut Rocks, at: F, x_len: usize, y_len: usize) 
+where F: Fn(&mut Rocks, usize, usize) -> &mut u8 {
+    (0..x_len).for_each(|x| { (0..y_len).for_each(|y| print!("{}", *at(rocks, x, y) as char)); println!() });
+}
+fn weigh<F>(rocks: &mut Rocks, at: F, x_len: usize, y_len: usize) -> usize
+where F: Fn(&mut Rocks, usize, usize) -> &mut u8 {
+    let mut weight: usize = 0;
+    (0..x_len).for_each(|x| (0..y_len).for_each(|y| if *at(rocks, x, y) == 'O' as u8 { weight += y_len - y }) );
+    return weight;
+}
+
+fn main() {
+    // let input = "example.txt";
+    let input = "input.txt";
+    let lines = read_lines(&input);
+    let mut original: Rocks = Vec::new();
+    for line in lines.map(|r| r.ok().unwrap()) {
+        original.push(line.chars().map(|c| c as u8).collect());
+    }
+    let ew_xlen = original.len();
+    let ew_ylen = original[0].len();
+    let ns_xlen = ew_ylen;
+    let ns_ylen = ew_xlen;
+
+    // TASK 1
+    let mut rocks = original.clone();
+    tilt(&mut rocks, north_at, ns_xlen, ns_ylen);
+    println!("Load on north support beams (1): {}", weigh(&mut rocks, north_at, ns_xlen, ns_ylen));
+    // print(&mut rocks, west_at, ew_xlen, ew_ylen);
+
+    // TASK 2
+    rocks = original.clone();
+    // find a cycle
+    let mut rocks_store: Vec<Rocks> = Vec::new();
+    let mut cycle_start: usize = 0;
+    let mut cycle_length: usize = 0;
+    for i in 0..1_000_000_000 as usize {
+        tilt(&mut rocks, north_at, ns_xlen, ns_ylen);
+        tilt(&mut rocks, west_at, ew_xlen, ew_ylen);
+        tilt(&mut rocks, south_at, ns_xlen, ns_ylen);
+        tilt(&mut rocks, east_at, ew_xlen, ew_ylen);
+        if let Some(j) = rocks_store.iter().position(|r| r.eq(&rocks)) {
+            cycle_start = j;
+            cycle_length = i - j;
+            println!("Cycle found! rocks at {} == rocks at {}", i, j);
+            break;
+        }
+        rocks_store.push(rocks.clone());
+    }
+    // do the cycles that remain after the ... Cycle
+    for _ in 0..(1_000_000_000 as usize - cycle_start) % cycle_length - 1 {
+        tilt(&mut rocks, north_at, ns_xlen, ns_ylen);
+        tilt(&mut rocks, west_at, ew_xlen, ew_ylen);
+        tilt(&mut rocks, south_at, ns_xlen, ns_ylen);
+        tilt(&mut rocks, east_at, ew_xlen, ew_ylen);
+    }
+    // tilt(&mut rocks, north_at, ns_xlen, ns_ylen);
+    println!("Load on north support beams (2): {}", weigh(&mut rocks, north_at, ns_xlen, ns_ylen));
+}
+
+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

@@ -16,5 +16,6 @@ This is a repository for my solutions for the [advent of code 2023](https://adve
 | [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           |
+| [14](14) | Rust     | 84            | 0,171 s         | no bruteforce in < 90 lines   |
 
  Lines of code are without blank lines and comments