day 03

src/aoc2021/day03/mod.rs

@@ -0,0 +1,110 @@
+const BITS_PER_LINE: usize = 12;
+
+pub fn task_one(input: &str) -> String {
+    let mut bit_amount: [(usize, usize); BITS_PER_LINE] = [(0, 0); BITS_PER_LINE];
+
+    for line in input.lines() {
+        for (i, c) in line.chars().enumerate() {
+            match c {
+                '0' => bit_amount[i] = (bit_amount[i].0 + 1, bit_amount[i].1),
+                '1' => bit_amount[i] = (bit_amount[i].0, bit_amount[i].1 + 1),
+                _ => panic!()
+            }
+        }
+    }
+
+    let mut gamma: usize = 0;
+    let mut epsilon: usize = 0;
+
+    for i in 0..BITS_PER_LINE {
+        if bit_amount[i].1 > bit_amount[i].0 {
+            gamma |= 0b1 << (BITS_PER_LINE - 1 - i);
+        } else {
+            epsilon |= 0b1 << (BITS_PER_LINE - 1 - i);
+        }
+    }
+
+    (gamma * epsilon).to_string()
+}
+
+pub fn task_two(input: &str) -> String {
+    // fyi, indices for binary representation start for me at 0 -> 0110 0011
+    // [0] = 1, [1] = 1, [2] = 0, ...
+    fn count_bits_at(vec: &Vec<usize>, pos: usize) -> (usize, usize) {
+        let mut bit_amount: (usize, usize) = (0, 0);
+
+        for number in vec.iter() {
+            if number & 1 << pos == 0 {
+                bit_amount = (bit_amount.0 + 1, bit_amount.1);
+            } else {
+                bit_amount = (bit_amount.0, bit_amount.1 + 1);
+            }
+        }
+
+        bit_amount
+    }
+
+    fn remove_numbers_with_bit_at(vec: &mut Vec<usize>, bit: usize, pos: usize) {
+        let mut i = 0;
+        if bit == 0 {
+            while i < vec.len() {
+                if vec[i] & 1 << pos == 0 {
+                    vec.remove(i);
+                } else {
+                    i += 1;
+                }
+            }
+        } else if bit == 1 {
+            while i < vec.len() {
+                if vec[i] & 1 << pos != 0 {
+                    vec.remove(i);
+                } else {
+                    i += 1;
+                }
+            }
+        }
+    }
+    
+    let mut oxgen_rating: usize = 0;
+    let mut coscrub_rating: usize = 0;
+
+    let mut numbers: Vec<usize> = Vec::new();
+    input.lines().for_each(|line| numbers.push(usize::from_str_radix(line, 2).expect("Error parsing string into usize")));
+
+    let mut oxgen_numbers = numbers.clone();
+    let mut coscrub_numbers = numbers.clone();
+
+    for i in 0..BITS_PER_LINE {
+        let pos = BITS_PER_LINE - 1 - i;
+        let oxgen_count = count_bits_at(&oxgen_numbers, pos);
+
+        if oxgen_count.1 >= oxgen_count.0 {
+            remove_numbers_with_bit_at(&mut oxgen_numbers, 0, pos);
+        } else {
+            remove_numbers_with_bit_at(&mut oxgen_numbers, 1, pos);
+        }
+
+        if oxgen_numbers.len() == 1 {
+            oxgen_rating = *oxgen_numbers.first().unwrap();
+            break;
+        }
+    }
+
+    for i in 0..BITS_PER_LINE {
+        let pos = BITS_PER_LINE - 1 - i;
+        let coscrub_count = count_bits_at(&coscrub_numbers, pos);
+
+        if coscrub_count.0 <= coscrub_count.1 {
+            remove_numbers_with_bit_at(&mut coscrub_numbers, 1, pos);
+        } else {
+            remove_numbers_with_bit_at(&mut coscrub_numbers, 0, pos);
+        }
+
+        if coscrub_numbers.len() == 1 {
+            coscrub_rating = *coscrub_numbers.first().unwrap();
+            break;
+        }
+    }
+
+    (oxgen_rating * coscrub_rating).to_string()
+}

src/aoc2021/mod.rs

@@ -1,2 +1,3 @@
 pub mod day01;
 pub mod day02;
+pub mod day03;

src/main.rs

@@ -13,4 +13,9 @@ fn main() {
     let result_day02_task1 = aoc2021::day02::task_one(&input_day02);
     let result_day02_task2 = aoc2021::day02::task_two(&input_day02);
     println!("AOC2021 Day 02 \t Task 1: {},\tTask 2: {}", result_day02_task1, result_day02_task2);
+
+    let input_day03 = fs::read_to_string("src/aoc2021/day03/input.txt").expect("Error on reading file.");
+    let result_day03_task1 = aoc2021::day03::task_one(&input_day03);
+    let result_day03_task2 = aoc2021::day03::task_two(&input_day03);
+    println!("AOC2021 Day 03 \t Task 1: {},\tTask 2: {}", result_day03_task1, result_day03_task2);
 }