add day 16

day16/src/main.rs

@@ -0,0 +1,50 @@
+use itertools::Itertools;
+
+#[cfg(debug_assertions)]
+const INPUT: usize = 10000;
+#[cfg(debug_assertions)]
+const LENGTH: usize = 20;
+
+#[cfg(not(debug_assertions))]
+const INPUT: usize = 10011111011011001;
+#[cfg(not(debug_assertions))]
+const LENGTH: usize = 272;
+const LENGTH2: usize = 35651584;
+
+fn main() {
+    calculate_checksum(LENGTH);
+    calculate_checksum(LENGTH2);
+}
+
+fn calculate_checksum(length: usize) {
+    let mut a = INPUT.to_string();
+    while a.len() < length {
+        let mut b = a.clone();
+        b = b
+            .chars()
+            .rev()
+            .map(|c| if c == '0' { '1' } else { '0' })
+            .collect();
+
+        let mut result = a.clone();
+        result.push('0');
+        result.push_str(&b);
+        a = result;
+    }
+    a.truncate(length);
+
+    loop {
+        let possible_checksum: String = a
+            .chars()
+            .tuples()
+            .map(|(c0, c1)| c0 == c1)
+            .map(|b| if b { '1' } else { '0' })
+            .collect();
+        if possible_checksum.len() % 2 == 1 {
+            a = possible_checksum;
+            break;
+        }
+        a = possible_checksum;
+    }
+    println!("{a}");
+}