Added Jarvis March for C++ (#283)

* Added cpp file

* Added Gorzoid to CONTRIBUTORS.md

* Fixed style to conform with guidelines #18

* Removed unnecessary define

* Added entry to jarvis_march.md

* Added check for empty array edge case. Changed Iterators to single vector reference

* Changed to resolve edge case of duplicate points.

Author: Gorzoid

CONTRIBUTORS.md

@@ -48,8 +48,10 @@ Max Weinstein
 <br>
 Gibus Wearing Brony
 <br>
+Gorzoid
+<br>
 Arun Sahadeo
 <br>
 NIFR91
 <br>
-Michal Hanajik
+Michal Hanajik

contents/jarvis_march/code/c++/jarvis_march.cpp

@@ -0,0 +1,72 @@
+#include <vector>
+#include <iostream>
+#include <algorithm>
+
+struct Point
+{
+    double x, y;
+
+    bool operator==(const Point& b) const
+    {
+        return x == b.x && y == b.y;
+    }
+
+    bool operator!=(const Point& b) const
+    {
+        return !(*this == b);
+    }
+};
+
+std::vector<Point> jarvis_march(const std::vector<Point>& points)
+{
+    std::vector<Point> hull_points;
+
+    if(points.empty())
+        return hull_points;
+
+    // Left most point
+    auto first_point_it = std::min_element(points.begin(), points.end(), [](const Point& a, const Point& b){ return a.x < b.x; });
+
+    auto next_point_it = first_point_it;
+    do
+    {
+        hull_points.push_back(*next_point_it);
+
+        const Point& p1 = hull_points.back();
+
+        // Largest internal angle
+        next_point_it = std::max_element(
+            points.begin(),
+            points.end(),
+            [p1](const Point& p2, const Point& p3){
+                return (p1 == p2) || (p2.x - p1.x) * (p3.y - p1.y) > (p3.x - p1.x) * (p2.y - p1.y);
+            }
+        );
+    }
+    while(*next_point_it != *first_point_it);
+
+    return hull_points;
+}
+
+int main() {
+    std::vector<Point> points = {
+        { 1.0, 3.0 },
+        { 1.0, 3.0 },
+        { 2.0, 4.0 },
+        { 4.0, 0.0 },
+        { 1.0, 0.0 },
+        { 0.0, 2.0 },
+        { 2.0, 2.0 },
+        { 3.0, 4.0 },
+        { 3.0, 1.0 },
+    };
+
+    auto hull_points = jarvis_march(points);
+
+    std::cout << "Hull points are:" << std::endl;
+
+    for(const Point& point : hull_points) {
+        std::cout << '(' << point.x << ", " << point.y << ')' << std::endl;
+    }
+}
+

contents/jarvis_march/jarvis_march.md

@@ -38,6 +38,8 @@ Program.cs
 [import, lang:"javascript"](code/javascript/jarvis-march.js)
 {% sample lang="py" %}
 [import, lang:"python"](code/python/jarvisMarch.py)
+{% sample lang="cpp" %}
+[import, lang:"c_cpp"](code/c++/jarvis_march.cpp)
 {% endmethod %}
 
 <script>