From 74592d2b32598f9718337fcd833f1baff82d2cef Mon Sep 17 00:00:00 2001
From: "Dr. Matthias Ratajczak" <m.ratajczak@hzdr.de>
Date: Fri, 23 Sep 2022 17:56:02 +0200
Subject: [PATCH] finish 81

---
 src/euler81/p081_test.txt |   5 ++
 src/euler81/src/main.rs   | 129 +++++++++++++++++++++++++++++++-------
 2 files changed, 112 insertions(+), 22 deletions(-)
 create mode 100644 src/euler81/p081_test.txt

diff --git a/src/euler81/p081_test.txt b/src/euler81/p081_test.txt
new file mode 100644
index 0000000..76167d9
--- /dev/null
+++ b/src/euler81/p081_test.txt
@@ -0,0 +1,5 @@
+131,673,234,103,18
+201,96,342,965,150
+630,803,746,422,111
+537,699,497,121,956
+805,732,524,37,331
diff --git a/src/euler81/src/main.rs b/src/euler81/src/main.rs
index 9d1eab2..3e0b558 100644
--- a/src/euler81/src/main.rs
+++ b/src/euler81/src/main.rs
@@ -1,12 +1,19 @@
-use std::cell::RefCell;
 use std::collections::HashSet;
 use std::fs;
-use std::iter::Cycle;
 use std::path::Path;
-use std::rc::Rc;
 
+#[cfg(debug_assertions)]
+const LENGTH: usize = 5;
+
+#[cfg(not(debug_assertions))]
 const LENGTH: usize = 80;
 
+#[cfg(debug_assertions)]
+const FILENAME: &str = "p081_test.txt";
+
+#[cfg(not(debug_assertions))]
+const FILENAME: &str = "p081_matrix.txt";
+
 type Coordinate = (usize, usize);
 
 struct Matrix {
@@ -26,57 +33,135 @@ impl Matrix {
                     .collect()
             })
             .collect();
-        data[0][0].is_infinity = false;
+        let mut start = &mut data[0][0];
+        start.distance = Some(start.value);
         assert_eq!(data.len(), LENGTH);
         assert!(data.iter().all(|subvec| subvec.len() == LENGTH));
         Self { data }
     }
+
+    fn get(&self, c: &Coordinate) -> &Node {
+        &self.data[c.0][c.1]
+    }
 }
 
 fn main() {
-    let matrix = Matrix::load(Path::new("p081_matrix.txt"));
-    let dijkstra = Dijkstra::new(matrix);
+    let matrix = Matrix::load(Path::new(FILENAME));
+    let mut dijkstra = Dijkstra::new(matrix);
+    dijkstra.solve();
+    dijkstra.show();
 }
 
 struct Dijkstra {
-    initial: Coordinate,
     matrix: Matrix,
-    unvisited: Vec<Coordinate>,
+    unvisited: HashSet<Coordinate>,
 }
 
 impl Dijkstra {
     fn new(matrix: Matrix) -> Self {
-        let initial = (0, 0);
-        let unvisited: Vec<_> = (0..LENGTH)
+        let unvisited: HashSet<_> = (0..LENGTH)
             .flat_map(|x| (0..LENGTH).zip([x].into_iter().cycle()))
             .filter(|value| *value != (0, 0))
             .collect();
         assert_eq!(unvisited.len(), LENGTH * LENGTH - 1);
-        Self {
-            initial,
-            matrix,
-            unvisited,
+        Self { matrix, unvisited }
+    }
+
+    fn solve(&mut self) {
+        while !self.unvisited.is_empty() {
+            let coord = self.get_unvisited_coord_with_smallest_distance_from_start();
+            let neighbours = self.get_neighbours(&coord);
+            let previous_distance = self.matrix.get(&coord).distance.unwrap();
+            for neighbour in neighbours {
+                self.update_neighbour(neighbour, coord, previous_distance);
+            }
         }
     }
+
+    fn get_unvisited_coord_with_smallest_distance_from_start(&mut self) -> Coordinate {
+        let coord = self
+            .unvisited
+            .iter()
+            .filter_map(|c| {
+                let node = self.matrix.get(c);
+                node.distance.map(|value| (c, value))
+            })
+            .reduce(|(c0, v0), (c1, v1)| if v0 < v1 { (c0, v0) } else { (c1, v1) })
+            .map(|(c, _)| *c)
+            .unwrap_or((0, 0));
+        self.unvisited.remove(&coord);
+        coord
+    }
+
+    fn get_neighbours(&self, coordinate: &Coordinate) -> Vec<Coordinate> {
+        let (x0, y0) = coordinate;
+        let mut result = vec![];
+        if *x0 < LENGTH - 1 {
+            result.push((*x0 + 1, *y0));
+        }
+        if *y0 < LENGTH - 1 {
+            result.push((*x0, *y0 + 1));
+        }
+        result
+    }
+
+    fn update_neighbour(&mut self, next: Coordinate, previous: Coordinate, previous_distance: u32) {
+        let mut next_node = &mut self.matrix.data[next.0][next.1];
+        let new_distance = previous_distance + next_node.value;
+        match next_node.distance {
+            None => {
+                next_node.distance = Some(new_distance);
+                next_node.previous = Some(previous);
+            }
+            Some(old_distance) => {
+                if new_distance < old_distance {
+                    next_node.distance = Some(new_distance);
+                    next_node.previous = Some(previous);
+                }
+            }
+        }
+    }
+
+    fn show(&self) {
+        println!(
+            "{}",
+            self.matrix.data[LENGTH - 1][LENGTH - 1].distance.unwrap()
+        );
+    }
 }
 
 #[derive(PartialEq, Eq, Hash)]
 struct Node {
-    is_infinity: bool,
     value: u32,
+    distance: Option<u32>,
+    previous: Option<Coordinate>,
+}
+
+impl Node {
+    fn smaller_distance(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        match self.distance {
+            Some(v1) => match other.distance {
+                Some(v2) => v1.partial_cmp(&v2),
+                None => Some(std::cmp::Ordering::Less),
+            },
+            None => match other.distance {
+                Some(_) => Some(std::cmp::Ordering::Greater),
+                None => None,
+            },
+        }
+    }
+
+    // fn smaller_value(&self, other: &Self) -> Option<std::cmp::Ordering> {
+    //     self.value.partial_cmp(&other.value)
+    // }
 }
 
 impl From<u32> for Node {
     fn from(value: u32) -> Self {
         Node {
-            is_infinity: true,
             value,
+            distance: None,
+            previous: None,
         }
     }
 }
-
-impl From<Node> for Rc<RefCell<Node>> {
-    fn from(node: Node) -> Self {
-        Rc::new(RefCell::new(node))
-    }
-}