Day 20 2022

3 files changed, 53 insertions, 0 deletions

diff --git a/2022/20/a.rs b/2022/20/a.rs
new file mode 100644
index 0000000..0b80099
--- /dev/null
+++ b/2022/20/a.rs
@@ -0,0 +1,8 @@
+mod common;
+use common::*;
+
+fn main() {
+    let mut a = read_from_stdin(1);
+    mix(&mut a);
+    println!("{}", groove_sum(&a));
+}
diff --git a/2022/20/b.rs b/2022/20/b.rs
new file mode 100644
index 0000000..ec10cf0
--- /dev/null
+++ b/2022/20/b.rs
@@ -0,0 +1,8 @@
+mod common;
+use common::*;
+
+fn main() {
+    let mut a = read_from_stdin(811589153);
+    for _ in 0..10 { mix(&mut a); }
+    println!("{}", groove_sum(&a));
+}
diff --git a/2022/20/common.rs b/2022/20/common.rs
new file mode 100644
index 0000000..cecc316
--- /dev/null
+++ b/2022/20/common.rs
@@ -0,0 +1,37 @@
+const MAX_OVERFLOW: i64 = 10000000000;
+
+pub fn read_from_stdin(key: i64) -> Vec<(usize, i64)> {
+    let mut line = String::new();
+    let mut v = vec![];
+    while std::io::stdin().read_line(&mut line).unwrap() > 0 {
+        v.push((v.len(), line[..line.len()-1].parse::<i64>().unwrap() * key));
+        line.clear();
+    }
+    v
+}
+
+fn get_newpos(pos: i64, k: i64, n: i64) -> i64 {
+    (pos + k + MAX_OVERFLOW * (n-1)) % (n-1)
+}
+
+fn move_to(a: &mut [(usize, i64)], i: usize, j: usize) {
+    if i < j {
+        for k in i..j { a.swap(k, k+1); }
+    } else {
+        for k in (j+1..=i).rev() { a.swap(k, k-1); }
+    }
+}
+
+pub fn mix(a: &mut Vec<(usize, i64)>) {
+    for i in 0..a.len() {
+        let pos = a.iter().position(|x| x.0 == i).unwrap();
+        let newpos = get_newpos(pos as i64, a[pos].1, a.len() as i64) as usize;
+        move_to(a, pos, newpos);
+    }
+}
+
+pub fn groove_sum(a: &Vec<(usize, i64)>) -> i64 {
+    let n = a.len();
+    let z = a.iter().position(|x| x.1 == 0).unwrap();
+    a[(z + 1000) % n].1 +  a[(z + 2000) % n].1 + a[(z + 3000) % n].1
+}