Implement Graham Scan in Rust (algorithm-archivists#964)

* Implement Graham Scan in Rust

* Add Thijs

* Remove compiled binary

* Define ordering of points for sorting

* Clean up code

* Change points to match other implementations

* Apply requested changes from algorithm-archivists#479

* Fix function signature

* Add function comment

* Change algorithm to simpler version from python

* Fix points to match other languages

* Adjust line numbers for rust

* Apply clippy suggestions

Co-authored-by: Thijs Raymakers <[email protected]>
Co-authored-by: Sammy Plat <[email protected]>
Co-authored-by: Dimitri Belopopsky <[email protected]>

CONTRIBUTORS.md

@@ -63,3 +63,4 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - Henrik Abel Christensen
 - K. Shudipto Amin
 - Peanutbutter_Warrior
+- Thijs Raymakers 

contents/graham_scan/code/rust/graham_scan.rs

@@ -0,0 +1,84 @@
+use std::cmp::Ordering;
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+struct Point {
+    x: f64,
+    y: f64,
+}
+
+impl Eq for Point {}
+
+impl PartialOrd for Point {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        if self.y == other.y {
+            self.x.partial_cmp(&other.x)
+        } else {
+            self.y.partial_cmp(&other.y)
+        }
+    }
+}
+
+// Defines an order for Points so they can be sorted
+impl Ord for Point {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // Neither field of Point will be NaN, so this is safe
+        self.partial_cmp(other).unwrap()
+    }
+}
+
+// Determines whether the angle abc is clockwise, counter-clockwise or colinear
+// result > 0 : counter-clockwise
+// result = 0 : colinear
+// result < 0 : clockwise
+fn counter_clockwise(a: &Point, b: &Point, c: &Point) -> f64 {
+    (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x)
+}
+
+// Calculate the polar angle of a  point relative to a reference point.
+fn polar_angle(reference: &Point, point: &Point) -> f64 {
+    (point.y - reference.y).atan2(point.x - reference.x)
+}
+
+fn graham_scan(mut points: Vec<Point>) -> Vec<Point> {
+    if points.is_empty() {
+        return Vec::new();
+    }
+
+    // Unwrap is safe because length is > 0
+    let start = *points.iter().min().unwrap();
+    points.retain(|a| a != &start);
+    points.sort_unstable_by(|a, b| polar_angle(&start, a).partial_cmp(&polar_angle(&start, b)).unwrap());
+
+    let mut hull: Vec<Point> = vec![start, points[0], points[1]];
+
+    for pt in points[2..points.len()].iter() {
+        while counter_clockwise(&hull[hull.len() - 2], &hull[hull.len() - 1], pt) < 0.0 {
+            hull.pop();
+        }
+        hull.push(*pt);
+    }
+    hull
+}
+
+fn main() {
+    let points = vec![
+        Point { x:  -5.0, y:   2.0 },
+        Point { x:   5.0, y:   7.0 },
+        Point { x:  -6.0, y: -12.0 },
+        Point { x: -14.0, y: -14.0 },
+        Point { x:   9.0, y:   9.0 },
+        Point { x:  -1.0, y:  -1.0 },
+        Point { x: -10.0, y:  11.0 },
+        Point { x:  -6.0, y:  15.0 },
+        Point { x:  -6.0, y:  -8.0 },
+        Point { x:  15.0, y:  -9.0 },
+        Point { x:   7.0, y:  -7.0 },
+        Point { x:  -2.0, y:  -9.0 },
+        Point { x:   6.0, y:  -5.0 },
+        Point { x:   0.0, y:  14.0 },
+        Point { x:   2.0, y:   8.0 },
+    ];
+
+    let hull_points = graham_scan(points);
+    println!("{:#?}", hull_points);
+}

contents/graham_scan/graham_scan.md

@@ -32,6 +32,8 @@ We can find whether a rotation is counter-clockwise with trigonometric functions
 [import:18-20, lang="cpp"](code/cpp/graham_scan.cpp)
 {% sample lang="coco" %}
 [import:4-8, lang="coconut"](code/coconut/graham_scan.coco)
+{% sample lang="rs" %}
+[import:33-35, lang: "rust"](code/rust/graham_scan.rs)
 {% endmethod %}
 
 If the output of this function is 0, the points are collinear.
@@ -66,6 +68,8 @@ In the end, the code should look something like this:
 [import:26-62, lang="cpp"](code/cpp/graham_scan.cpp)
 {% sample lang="coco" %}
 [import:17-30, lang="coconut"](code/coconut/graham_scan.coco)
+{% sample lang="rs" %}
+[import:42-61, lang: "rust"](code/rust/graham_scan.rs)
 {% endmethod %}
 
 ### Bibliography
@@ -95,6 +99,8 @@ In the end, the code should look something like this:
 [import, lang="cpp"](code/cpp/graham_scan.cpp)
 {%sample lang="coco" %}
 [import, lang="coconut"](code/coconut/graham_scan.coco)
+{% sample lang="rs" %}
+[import, lang: "rust"](code/rust/graham_scan.rs)
 {% endmethod %}
 
 <script>