1 files changed, 71 insertions, 0 deletions
diff --git a/src/day1.rs b/src/day1.rs
index 1326af6..1685dbd 100644
--- a/src/day1.rs
+++ b/src/day1.rs
@@ -1,5 +1,6 @@
 use aoc_runner_derive::*;
 use std::str::FromStr;
+use std::ops::Add;
 
 #[aoc_generator(day1)]
 pub fn input_generator<'c>(input : &'c str) -> Vec<u32>{ 
@@ -57,3 +58,73 @@ pub fn solve_part2_iterators(input : &Vec<u32>) -> usize {
     let sliding_window = sliding_window.skip(1);
     sliding_window.zip(old_window).filter(|(new, old)| new > old).count()
 }
+
+enum FloatingWindow {
+    Prewarming{
+        value : u32,
+        previous : [u32;2],
+        index : usize,
+    },
+    Ready{
+        value : u32,
+        previous : [u32;3],
+        index : usize,
+    },
+}
+
+impl FloatingWindow {
+    fn try_get(&self) -> Option<u32> {
+        match self {
+            FloatingWindow::Prewarming{..} => { None }
+            FloatingWindow::Ready{value, ..} => { Some(*value) }
+        }
+    }
+}
+
+impl Default for FloatingWindow {
+    fn default() -> Self {
+        FloatingWindow::Prewarming{value:0,previous:[0;2],index:0}
+    }
+}
+
+impl Add<u32> for FloatingWindow {
+    type Output = FloatingWindow;
+    fn add(self, rhs : u32) -> FloatingWindow {
+        match self {
+            FloatingWindow::Prewarming{value, previous, index} if index < 2 => {
+                let mut arr = previous;
+                arr[index] = rhs;
+                FloatingWindow::Prewarming{value: value + rhs, previous : arr, index: index + 1}
+            }
+            FloatingWindow::Prewarming{value, previous, index} => {
+                let arr = [previous[0], previous[1], rhs];
+                FloatingWindow::Ready{value: value + rhs, previous : arr, index: 0}
+            }
+            FloatingWindow::Ready{value, previous, index} => {
+                let mut arr = previous;
+                let old = arr[index];
+                arr[index] = rhs;
+                FloatingWindow::Ready{value: (value + rhs - old), previous : arr, index: (index + 1)%3}
+            }
+        }
+    }
+}
+#[aoc(day1, part2, AccumulatorType)]
+pub fn solve_part2_accumulator_type(input : &Vec<u32>) -> u32 {
+    struct Helper {
+        floating_window : FloatingWindow,
+        prev : Option<u32>,
+        count : u32,
+    }
+    input.iter()
+        .fold(
+            Helper{floating_window : FloatingWindow::default(), prev : None, count: 0}, 
+            |Helper{floating_window, prev, count}, i| {
+                let prev = floating_window.try_get();
+                let floating_window = floating_window + *i;
+                let curr = floating_window.try_get();
+                let count = count + prev.zip(curr).and_then(|(prev,curr)| (curr > prev).then(|| 1)).unwrap_or(0);
+                Helper{floating_window, prev, count}
+            }
+        ).count
+}