📅  最后修改于: 2023-12-03 15:22:24.589000             🧑  作者: Mango
旋转卡尺方法是一种求解点集凸壳的算法,其基本思想是绕点集的凸壳旋转卡尺,在旋转过程中去寻找距离最远的两个点。这种算法可以采用两个指针分别指向凸壳上的两个点,然后不断旋转卡尺直到两个指针重合,期间记录下距离最大的两点距离即可。
def cal_distance(p1, p2):
"""
计算两个点之间的欧几里得距离
"""
return ((p1[0]-p2[0])**2 + (p1[1]-p2[1])**2)**0.5
def rotating_calipers(points):
"""
旋转卡尺算法
points: 点的坐标列表,每个元素是一个 tuple (x, y)
return: 最大距离
"""
n = len(points)
if n < 2:
return 0
# 排序,记录起始点和当前最大距离
points.sort()
p1, p2 = points[0], points[-1]
max_distance = cal_distance(p1, p2)
# 初始化旋转卡尺,首先定义向量 (1, 0)
v_start = (1, 0)
i, j = 0, n-1
while i < j:
# 旋转卡尺,通过向量积来判断当前点和向量的相对方向
v_tmp = (points[i+1][0]-points[i][0], points[i+1][1]-points[i][1])
v_rotate = (-v_tmp[1], v_tmp[0])
while j > i+1:
v_p = (points[j][0]-points[i][0], points[j][1]-points[i][1])
if v_rotate[0]*v_p[0] + v_rotate[1]*v_p[1] > 0:
break
j -= 1
# 计算当前点和p1、p2之间的距离,更新最大距离
cur_distance = cal_distance(points[i], p1)
if cur_distance > max_distance:
max_distance = cur_distance
p2 = points[i]
cur_distance = cal_distance(points[j], p2)
if cur_distance > max_distance:
max_distance = cur_distance
p1 = points[j]
i += 1
return max_distance