2017, day 25

Author: alokmenghrajani

src/main.rs

@@ -93,6 +93,7 @@ fn main() {
         (2017, 22) => year_2017::day22::run(inputs::read(year, day)),
         (2017, 23) => year_2017::day23::run(inputs::read(year, day)),
         (2017, 24) => year_2017::day24::run(inputs::read(year, day)),
+        (2017, 25) => year_2017::day25::run(),
 
         // Other
         (_, _) => panic!("Not implemented :("),

src/year_2017/day25.rs

@@ -0,0 +1,78 @@
+use std::collections::HashMap;
+
+pub fn run() {
+    // For the last day, it was easier to directly convert the input into cod else
+    // multi-selection to the rescue!
+    let mut pos = 0;
+    let mut state = 'A';
+    let mut tape: HashMap<i64, i64> = HashMap::new();
+
+    for _ in 0..12629077 {
+        let t = tape.entry(pos).or_insert(0);
+        if state == 'A' {
+            if *t == 0 {
+                *t = 1;
+                pos += 1;
+                state = 'B';
+            } else {
+                *t = 0;
+                pos -= 1;
+                state = 'B';
+            }
+        } else if state == 'B' {
+            if *t == 0 {
+                *t = 0;
+                pos += 1;
+                state = 'C';
+            } else {
+                *t = 1;
+                pos -= 1;
+                state = 'B';
+            }
+        } else if state == 'C' {
+            if *t == 0 {
+                *t = 1;
+                pos += 1;
+                state = 'D';
+            } else {
+                *t = 0;
+                pos -= 1;
+                state = 'A';
+            }
+        } else if state == 'D' {
+            if *t == 0 {
+                *t = 1;
+                pos -= 1;
+                state = 'E';
+            } else {
+                *t = 1;
+                pos -= 1;
+                state = 'F';
+            }
+        } else if state == 'E' {
+            if *t == 0 {
+                *t = 1;
+                pos -= 1;
+                state = 'A';
+            } else {
+                *t = 0;
+                pos -= 1;
+                state = 'D';
+            }
+        } else if state == 'F' {
+            if *t == 0 {
+                *t = 1;
+                pos += 1;
+                state = 'A';
+            } else {
+                *t = 1;
+                pos -= 1;
+                state = 'E';
+            }
+        }
+    }
+
+    let sum: i64 = tape.values().sum();
+    println!("part 1: {}", sum);
+    assert_eq!(sum, 3745);
+}

src/year_2017/mod.rs

@@ -22,3 +22,4 @@ pub mod day21;
 pub mod day22;
 pub mod day23;
 pub mod day24;
+pub mod day25;