check-point-in-tringle.py

# -*- coding: utf-8 -*-


def cross_product(p1, p2, p3):
    return ((p1[0] - p3[0]) * (p2[1] - p3[1])) - ((p2[0] - p3[0]) * (p1[1] - p3[1]))


def point_in_triangle(s, p1, p2, p3):
    b1 = cross_product(s, p1, p2) < 0
    b2 = cross_product(s, p2, p3) < 0
    b3 = cross_product(s, p3, p1) < 0
    return (b1 == b2 and b2 == b3)

if __name__ == "__main__":
    print point_in_triangle([10, 10], [0, 0], [3, 0], [0, 4])
    print point_in_triangle([1, 1], [0, 0], [3, 0], [0, 4])