Implemented Graham's convex hull algorithm

Author: KyattPL

algorithms/GrahamAlgorithm.py

@@ -0,0 +1,65 @@
+from math import atan2, sqrt
+from pointPosition import position
+
+
+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+
+lowest_point = None
+
+
+def angle(point):
+    return atan2(point.y - lowest_point.y, point.x - lowest_point.x)
+
+
+def distance(point):
+    return sqrt((point.x - lowest_point.x)**2 + (point.y - lowest_point.y)**2)
+
+
+def find_lowest(points):
+    temp_low = points[0]
+    minimum = float("inf")
+    for p in points:
+        if p.y < minimum:
+            temp_low = p
+            minimum = p.y
+        elif p.y == minimum and p.x < temp_low.x:
+            temp_low = p
+    global lowest_point
+    lowest_point = temp_low
+
+
+def graham(points):
+    points = sorted(points, key=lambda x: (angle(x), distance(x)))
+    stack = []
+    stack.append(points[0])
+    stack.append(points[1])
+    stack.append(points[2])
+    for i in range(3, len(points)):
+        while position(stack[-1], stack[-2], points[i]) == 2:
+            stack.pop()
+        stack.append(points[i])
+    return stack
+
+
+if __name__ == "__main__":
+    points = []
+    p1 = Point(3, 8)
+    p2 = Point(1, 4)
+    p3 = Point(2, 5)
+    p4 = Point(7, 2)
+    p5 = Point(3, 2)
+    p6 = Point(5, 4)
+    points.append(p1)
+    points.append(p2)
+    points.append(p3)
+    points.append(p4)
+    points.append(p5)
+    points.append(p6)
+    find_lowest(points)
+    hull = graham(points)
+    for point in hull:
+        print("Point x: " + str(point.x) + ", y: " + str(point.y))

algorithms/pointPosition.py

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+# Given three points on a plane, determine the position of the third
+# point relative to p->q vector.
+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+
+def position(p, q, r):
+    first = p.x * q.y * 1
+    second = q.x * r.y * 1
+    third = r.x * p.y * 1
+    part1 = first + second + third
+
+    fourth = 1 * q.y * r.x
+    fifth = 1 * r.y * p.x
+    sixth = 1 * p.y * q.x
+    part2 = fourth + fifth + sixth
+
+    result = part1 - part2
+    if result > 0:
+        return 2
+    elif result < 0:
+        return 1
+    else:
+        return 0
+
+
+if __name__ == "__main__":
+    p = Point(5, 4)
+    q = Point(3, 2)
+    r = Point(6, 7)
+    outcome = position(p, q, r)
+    if outcome == 2:
+        print("Point r is on the left side of pq vector")
+    elif outcome == 1:
+        print("Point r is on the right side of the pq vector")
+    else:
+        print("Point r is on the same line as pq vector")