Python implementation for Jarvis March (#223)

* Added python3 example for Jarvis March.
* Added name to contributors

Author: wmboyles

CONTRIBUTORS.md

@@ -38,3 +38,5 @@ lulucca12
 <br>
 GuyPozner
 <br>
+William Boyles
+<br>

chapters/computational_geometry/gift_wrapping/jarvis_march/code/py/jarvisMarch.py

@@ -0,0 +1,38 @@
+# Is the turn counter clockwise?
+def CCW(p1, p2, p3):
+    return (p3[1]-p1[1])*(p2[0]-p1[0]) >= (p2[1]-p1[1])*(p3[0]-p1[0])
+
+
+def jarvisMarch(gift):
+    n = len(gift)  #Number of points in list
+    pointOnHull = min(gift) #leftmost point in gift
+    hull = [pointOnHull] #leftmost point guaranteed to be in hull
+    
+    while True:
+        endpoint = gift[0]  #Candidate for next point in hull
+        for j in range(1,n):
+            if endpoint==pointOnHull or not CCW(gift[j],hull[-1],endpoint):
+                endpoint = gift[j]
+                
+        pointOnHull = endpoint        
+                
+        #Check if we have completely wrapped gift
+        if hull[0]==endpoint:
+            break
+        else:
+            hull.append(pointOnHull)
+        
+    return hull
+
+
+def main():
+    testGift = [(5, 7), (5, 7), (-6, -12), (-14, -14), (9, 9), 
+                (-1, -1), (-10, 11), (-6, 15), (-6, -8), (15, -9),
+                (7, -7), (-2, -9), (6, -5), (0, 14), (2, 8)]
+    hull = jarvisMarch(testGift)
+    
+    print("The points in the hull are:")
+    for point in hull:
+        print(point)
+
+main()

chapters/computational_geometry/gift_wrapping/jarvis_march/jarvis_march.md

@@ -41,6 +41,9 @@ Program.cs
 {% sample lang="js" %}
 ### JavaScript
 [import, lang:"javascript"](code/javascript/jarvis-march.js)
+{% sample lang="py" %}
+### Python
+[import, lang:"python"](code/py/jarvisMarch.py)
 {% endmethod %}
 
 <script>