From 7dcf1fe29e7983409027a69f0fa046f76874859b Mon Sep 17 00:00:00 2001
From: Dennis Kobert <dennis@kobert.dev>
Date: Fri, 20 Dec 2019 09:30:19 +0100
Subject: Introduce helper functions and factor out state struct

---
 src/solvers.rs | 48 ++++++++++++++++++++++++++++++++++++------------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/src/solvers.rs b/src/solvers.rs
index 52ad4c1..6df4b4a 100644
--- a/src/solvers.rs
+++ b/src/solvers.rs
@@ -62,7 +62,40 @@ pub struct Solver<T: num::PrimInt> {
     /// width
     pub w: u32,
     /// Use to store already used blocks as a bitmask
-    solve_stack: Vec<T>,
+    solve_stack: Vec<SaveState<T>>,
+}
+
+#[derive(Clone)]
+pub struct SaveState<T: num::PrimInt> {
+    pub bitmask: T,
+    pub index: u32,
+}
+
+impl<T: num::PrimInt> SaveState<T> {
+    pub fn new() -> Self {
+        Self {
+            bitmask: T::zero(),
+            index: 0,
+        }
+    }
+
+    pub fn set_bit(&mut self, stone: u32) {
+        self.bitmask =
+            self.bitmask | T::from(1 << stone).expect("Stone placing index out of bounds");
+    }
+
+    pub fn get_bit(&self, stone: u32) -> T {
+        self.bitmask & T::from(1 << stone).expect("Requested stone index out of bounds")
+    }
+
+    pub fn bridges_gap(&self, index: u32) -> bool {
+        self.get_bit(index - self.index) == T::zero()
+    }
+
+    pub fn bridge_gap(&mut self, index: u32) {
+        self.set_bit(index - self.index);
+        self.index = index
+    }
 }
 
 impl<T: num::PrimInt> Solver<T> {
@@ -73,7 +106,7 @@ impl<T: num::PrimInt> Solver<T> {
             n: (n as u32),
             h: (h as u32),
             w: (w as u32),
-            solve_stack: vec![T::zero(); h],
+            solve_stack: vec![SaveState::new(); h],
         }
     }
 
@@ -83,16 +116,7 @@ impl<T: num::PrimInt> Solver<T> {
             .iter()
             .take(2)
             .zip(0..1)
-            .for_each(|(x, i)| self.set_stone(*x as usize, i));
+            .for_each(|(x, i)| self.solve_stack[*x as usize].set_bit(i));
         wall
     }
-
-    fn set_stone(&mut self, row: usize, stone: u32) {
-        self.solve_stack[row] =
-            self.solve_stack[row] | T::from(1 << stone).expect("Stone placing index out of bounds");
-    }
-
-    fn get_stone(&self, row: usize, stone: u32) {
-        self.solve_stack[row] & T::from(1 << stone).expect("Requested stone index out of bounds");
-    }
 }
-- 
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