Create Convex_Hull.py

Convex Hull (Jarvis' algo)

Author: NishithD

algorithms/python/Convex_Hull.py

@@ -0,0 +1,107 @@
+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+
+def Left_index(points):
+   
+    minn = 0
+    for i in range(1, len(points)):
+        if points[i].x < points[minn].x:
+            minn = i
+        elif points[i].x == points[minn].x:
+            if points[i].y > points[minn].y:
+                minn = i
+    return minn
+
+
+def orient(p, q, r):
+
+  
+    val = (q.y - p.y) * (r.x - q.x) - \
+          (q.x - p.x) * (r.y - q.y)
+
+    if val == 0:
+        return 0
+    elif val > 0:
+        return 1
+    else:
+        return 2
+
+
+def convexHull(points, n):
+    # There must be at least 3 points
+    if n < 3:
+        return
+
+    # Find the leftmost point
+    l = Left_index(points)
+
+    hull = []
+
+ 
+    p = l
+    q = 0
+    while (True):
+
+        # Add current point to result
+        hull.append(p)
+        q = (p + 1) % n
+
+        for i in range(n):
+
+            if (orient(points[p],
+                            points[i], points[q]) == 2):
+                q = i
+
+      
+        p = q
+
+  
+        if (p == l):
+            break
+
+    # Print Result
+    yy=[]
+    for each in hull:
+        xx=[]
+        pin1,pin2 =(points[each].x, points[each].y)
+        xx.append(pin1)
+        xx.append(pin2)
+        yy.append(xx)
+    print(yy,"before")
+    list_final=sorted(yy, key=lambda k: [k[0], k[1]])
+    print(list_final,":after")
+    for i in range(len(list_final)):
+        print("({},{})".format(list_final[i][0], list_final[i][1]))
+
+points = []
+n = int(input())
+for _ in range(n):
+    string=input()
+    x = ''
+    y = ''
+    i = 1
+    cond = True
+    while cond:
+        if string[i] == (","):
+            cond = False
+            i += 1
+        else:
+            x += string[i]
+            i += 1
+
+    cond = True
+    while cond:
+        if string[i] == (")"):
+            cond = False
+        else:
+            y += string[i]
+            i += 1
+            # print(y)
+    X=int(x)
+    Y=int(y)
+    points.append(Point(X, Y))
+
+convexHull(points, len(points))