Problem:


Distance

For given two segments s1 and s2, print the distance between them.

s1 is formed by end points p0 and p1, and
s2 is formed by end points p2 and p3.

Input

The entire input looks like:

q (the number of queries)
1st query
2nd query
...
qth query

Each query consists of integer coordinates of end points of s1 and s2 in the following format:

xp0 yp0 xp1 yp1 xp2 yp2 xp3 yp3

Output

For each query, print the distance. The output values should be in a decimal fraction with an error less than 0.00000001.

Constraints

1 ≤ q ≤ 1000

-10000 ≤ xpi, ypi ≤ 10000

p0 &ne; p1 and
p2 &ne; p3.

Sample Input

3
0 0 1 0 0 1 1 1
0 0 1 0 2 1 1 2
-1 0 1 0 0 1 0 -1

Sample Output

1.0000000000
1.4142135624
0.0000000000



Sample input:
3
0 0 1 0 0 1 1 1
0 0 1 0 2 1 1 2
-1 0 1 0 0 1 0 -1


Sample output:
1.0000000000
1.4142135624
0.0000000000

Submission status: Accepted

Solution code:
import cmath
import os
import sys

if os.getenv("LOCAL"):
    sys.stdin = open("_in.txt", "r")

sys.setrecursionlimit(10 ** 9)
INF = float("inf")
IINF = 10 ** 18
MOD = 10 ** 9 + 7
# MOD = 998244353

PI = cmath.pi
TAU = cmath.pi * 2
EPS = 1e-8


class Point:
    """
    2次元空間上の点
    """

    def __init__(self, c: complex):
        self.c = c

    @property
    def x(self):
        return self.c.real

    @property
    def y(self):
        return self.c.imag

    @staticmethod
    def from_rect(x: float, y: float):
        return Point(complex(x, y))

    @staticmethod
    def from_polar(r: float, phi: float):
        return Point(cmath.rect(r, phi))

    def __add__(self, p):
        """
        :param Point p:
        """
        return Point(self.c + p.c)

    def __iadd__(self, p):
        """
        :param Point p:
        """
        self.c += p.c
        return self

    def __sub__(self, p):
        """
        :param Point p:
        """
        return Point(self.c - p.c)

    def __isub__(self, p):
        """
        :param Point p:
        """
        self.c -= p.c
        return self

    def __mul__(self, f: float):
        return Point(self.c * f)

    def __imul__(self, f: float):
        self.c *= f
        return self

    def __truediv__(self, f: float):
        return Point(self.c / f)

    def __itruediv__(self, f: float):
        self.c /= f
        return self

    def __repr__(self):
        return "({}, {})".format(round(self.x, 10), round(self.y, 10))

    def __neg__(self):
        return Point(-self.c)

    def __eq__(self, p):
        return abs(self.c - p.c) < EPS

    def __abs__(self):
        return abs(self.c)

    def dot(self, p):
        """
        内積
        :param Point p:
        :rtype: float
        """
        return self.x * p.x + self.y * p.y

    def det(self, p):
        """
        外積
        :param Point p:
        :rtype: float
        """
        return self.x * p.y - self.y * p.x

    def dist(self, p):
        """
        距離
        :param Point p:
        :rtype: float
        """
        return abs(self.c - p.c)

    def r(self):
        """
        原点からの距離
        :rtype: float
        """
        return abs(self.c)

    def phase(self):
        """
        原点からの角度
        :rtype: float
        """
        return cmath.phase(self.c)

    def angle(self, p, q):
        """
        p に向かってる状態から q まで反時計回りに回転するときの角度
        :param Point p:
        :param Point q:
        :rtype: float
        """
        return (cmath.phase(q.c - self.c) - cmath.phase(p.c - self.c)) % TAU

    def area(self, p, q):
        """
        p, q となす三角形の面積
        :param Point p:
        :param Point q:
        :rtype: float
        """
        return abs((p - self).det(q - self) / 2)

    def projection_point(self, p, q, allow_outer=False):
        """
        線分 pq を通る直線上に垂線をおろしたときの足の座標
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_1_A&lang=ja
        :param Point p:
        :param Point q:
        :param allow_outer: 答えが線分の間になくても OK
        :rtype: Point|None
        """
        diff_q = q - p
        # 答えの p からの距離
        r = (self - p).dot(diff_q) / abs(diff_q)
        # 線分の角度
        phase = diff_q.phase()

        ret = Point.from_polar(r, phase) + p
        if allow_outer or (p - ret).dot(q - ret) < EPS:
            return ret
        return None

    def reflection_point(self, p, q):
        """
        直線 pq を挟んで反対にある点
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_1_B&lang=ja
        :param Point p:
        :param Point q:
        :rtype: Point
        """
        # 距離
        r = abs(self - p)
        # pq と p-self の角度
        angle = p.angle(q, self)
        # 直線を挟んで角度を反対にする
        angle = (q - p).phase() - angle
        return Point.from_polar(r, angle) + p

    def on_segment(self, p, q, allow_side=True):
        """
        点が線分 pq の上に乗っているか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_1_C&lang=ja
        :param Point p:
        :param Point q:
        :param allow_side: 端っこでギリギリ触れているのを許容するか
        :rtype: bool
        """
        if not allow_side and (self == p or self == q):
            return False
        # 外積がゼロ: 面積がゼロ == 一直線
        # 内積がマイナス: p - self - q の順に並んでる
        return abs((p - self).det(q - self)) < EPS and (p - self).dot(q - self) < EPS


class Line:
    """
    2次元空間上の直線
    """

    def __init__(self, a: float, b: float, c: float):
        """
        直線 ax + by + c = 0
        """
        self.a = a
        self.b = b
        self.c = c

    @staticmethod
    def from_gradient(grad: float, intercept: float):
        """
        直線 y = ax + b
        :param grad: 傾き
        :param intercept: 切片
        :return:
        """
        return Line(grad, -1, intercept)

    @staticmethod
    def from_segment(p1, p2):
        """
        :param Point p1:
        :param Point p2:
        """
        a = p2.y - p1.y
        b = p1.x - p2.x
        c = p2.y * (p2.x - p1.x) - p2.x * (p2.y - p1.y)
        return Line(a, b, c)

    @property
    def gradient(self):
        """
        傾き
        """
        return INF if self.b == 0 else -self.a / self.b

    @property
    def intercept(self):
        """
        切片
        """
        return INF if self.b == 0 else -self.c / self.b

    def is_parallel_to(self, l):
        """
        平行かどうか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_A&lang=ja
        :param Line l:
        """
        # 法線ベクトル同士の外積がゼロ
        return abs(Point.from_rect(self.a, self.b).det(Point.from_rect(l.a, l.b))) < EPS

    def is_orthogonal_to(self, l):
        """
        直行しているかどうか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_A&lang=ja
        :param Line l:
        """
        # 法線ベクトル同士の内積がゼロ
        return abs(Point.from_rect(self.a, self.b).dot(Point.from_rect(l.a, l.b))) < EPS

    def intersection_point(self, l):
        """
        交差する点
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_B&lang=ja
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_C&lang=ja
        FIXME: 誤差が気になる。EPS <= 1e-9 だと CGL_2_B ダメだった。
        :param l:
        :rtype: Point|None
        """
        a1, b1, c1 = self.a, self.b, self.c
        a2, b2, c2 = l.a, l.b, l.c
        det = a1 * b2 - a2 * b1
        if abs(det) < EPS:
            # 並行
            return None
        x = (b1 * c2 - b2 * c1) / det
        y = (a2 * c1 - a1 * c2) / det
        return Point.from_rect(x, y)


class Segment:
    """
    2次元空間上の線分
    """

    def __init__(self, p1, p2):
        """
        :param Point p1:
        :param Point p2:
        """
        self.p1 = p1
        self.p2 = p2

    def norm(self):
        """
        線分の長さ
        """
        return abs(self.p1 - self.p2)

    def intersects_with(self, s, allow_side=True):
        """
        交差するかどうか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_B&lang=ja
        :param Segment s:
        :param allow_side: 端っこでギリギリ触れているのを許容するか
        """
        l1 = Line.from_segment(self.p1, self.p2)
        l2 = Line.from_segment(s.p1, s.p2)
        if l1.is_parallel_to(l2):
            # 並行なら線分の端点がもう片方の線分の上にあるかどうか
            return (s.p1.on_segment(self.p1, self.p2, allow_side) or
                    s.p2.on_segment(self.p1, self.p2, allow_side) or
                    self.p1.on_segment(s.p1, s.p2, allow_side) or
                    self.p2.on_segment(s.p1, s.p2, allow_side))
        else:
            # 直線同士の交点が線分の上にあるかどうか
            p = l1.intersection_point(l2)
            return p.on_segment(self.p1, self.p2, allow_side) and p.on_segment(s.p1, s.p2, allow_side)

    def closest_point(self, p):
        """
        線分上の、p に最も近い点
        :param Point p:
        """
        # p からおろした垂線までの距離
        d = (p - self.p1).dot(self.p2 - self.p1) / self.norm()
        # p1 より前
        if d < EPS:
            return self.p1
        # p2 より後
        if -EPS < d - self.norm():
            return self.p2
        # 線分上
        return Point.from_polar(d, (self.p2 - self.p1).phase()) + self.p1

    def dist(self, p):
        """
        他の点との最短距離
        :param Point p:
        """
        return abs(p - self.closest_point(p))

    def dist_segment(self, s):
        """
        他の線分との最短距離
        :param Segment s:
        """
        if self.intersects_with(s):
            return 0.0
        return min(
            self.dist(s.p1),
            self.dist(s.p2),
            s.dist(self.p1),
            s.dist(self.p2),
        )


Q = int(sys.stdin.buffer.readline())
ROWS = [list(map(int, sys.stdin.buffer.readline().split())) for _ in range(Q)]

for x0, y0, x1, y1, x2, y2, x3, y3 in ROWS:
    s1 = Segment(Point.from_rect(x0, y0), Point.from_rect(x1, y1))
    s2 = Segment(Point.from_rect(x2, y2), Point.from_rect(x3, y3))
    print(s1.dist_segment(s2))

Submission status: Accepted

Solution code:
#!/usr/bin/python3

import array
from fractions import Fraction
import math
import os
import sys


def main():
    Q = read_int()
    for _ in range(Q):
        x0, y0, x1, y1, x2, y2, x3, y3 = read_ints()
        print(solve(Vec(x0, y0), Vec(x1, y1), Vec(x2, y2), Vec(x3, y3)))


def pairwise_min2(a, b, c):
    return min(b.abs2(), c.abs2(),
               (b - a).abs2(), (c - a).abs2())


def calc3(a, b, c):
    c_ab = a.cross(b)
    c_ac = a.cross(c)
    if c_ab == 0 and c_ac == 0:  # on line
        s = Fraction(a.dot(b), a.abs2())
        t = Fraction(a.dot(c), a.abs2())
        if s < 0 and t < 0:
            return (max(s, t) * a).abs2()
        if s > 1 and t > 1:
            return ((min(s, t) - 1) * a).abs2()
        return 0

    cb = c - b
    c_acb = a.cross(cb)
    if c_acb != 0:  # not parallel
        u = Fraction(b.cross(cb), c_acb)
        v = Fraction(b.cross(a), c_acb)
        if 0 <= u <= 1 and 0 <= v <= 1:
            return 0  # crossed

    d_cba = cb.dot(a)
    if d_cba == 0:  # orthogonal
        s = Fraction(b.dot(a), a.abs2())
        if 0 <= s <= 1:
            sa = s * a
            return min((b - sa).abs2(), (c - sa).abs2())
        return pairwise_min2(a, b, c)

    d_ba = b.dot(a)
    d_ca = c.dot(a)
    a2 = a.abs2()
    s = Fraction(d_ba, a2)
    t = Fraction(d_ca, a2)
    p = Fraction(-d_ba, d_cba)
    q = Fraction(a2 - d_ba, d_cba)

    dists = [pairwise_min2(a, b, c)]
    if 0 <= s <= 1:
        dists.append((b - s * a).abs2())
    if 0 <= t <= 1:
        dists.append((c - t * a).abs2())
    if 0 <= p <= 1:
        dists.append((b + p * cb).abs2())
    if 0 <= q <= 1:
        dists.append((b + q * cb - a).abs2())

    return min(dists)


def solve(u, v, w, x):
    return math.sqrt(min(calc3(v - u, w - u, x - u),
                         calc3(x - w, u - w, v - w)))


###############################################################################
# AUXILIARY FUNCTIONS

class Vec(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
        super().__init__()

    def __add__(self, other):
        return Vec(self.x + other.x, self.y + other.y)

    def __sub__(self, other):
        return Vec(self.x - other.x, self.y - other.y)

    def __mul__(self, scalar):
        return Vec(self.x * scalar, self.y * scalar)

    def __rmul__(self, scalar):
        return Vec(self.x * scalar, self.y * scalar)

    def __truediv__(self, scalar):
        return Vec(self.x / scalar, self.y / scalar)

    def __iadd__(self, other):
        self.x += other.x
        self.y += other.y
        return self

    def __isub__(self, other):
        self.x -= other.x
        self.y -= other.y
        return self

    def __imul__(self, scalar):
        self.x *= scalar
        self.y *= scalar
        return self

    def __idiv__(self, scalar):
        self.x /= scalar
        self.y /= scalar
        return self

    def __neg__(self):
        return Vec(-self.x, -self.y)

    def dot(self, other):
        return self.x * other.x + self.y * other.y

    def cross(self, other):
        return self.x * other.y - self.y * other.x

    def abs2(self):
        return self.x * self.x + self.y * self.y

    def __abs__(self):
        return math.sqrt(float(self.abs2()))

    def __str__(self):
        return '({}, {})'.format(self.x, self.y)


DEBUG = 'DEBUG' in os.environ


def inp():
    return sys.stdin.readline().rstrip()


def read_int():
    return int(inp())


def read_ints():
    return [int(e) for e in inp().split()]


def dprint(*value, sep=' ', end='\n'):
    if DEBUG:
        print(*value, sep=sep, end=end)


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

import sys

sys.setrecursionlimit(10 ** 9)
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
INF=float('inf')

class Geometry:

    EPS = 10 ** -9

    def add(self, a, b):
        x1, y1 = a
        x2, y2 = b
        return (x1+x2, y1+y2)

    def sub(self, a, b):
        x1, y1 = a
        x2, y2 = b
        return (x1-x2, y1-y2)

    def mul(self, a, b):
        x1, y1 = a
        if not isinstance(b, tuple):
            return (x1*b, y1*b)
        x2, y2 = b 
        return (x1*x2, y1*y2)

    def abs(self, a):
        from math import hypot
        x1, y1 = a
        return hypot(x1, y1)

    def norm(self, a):
        x, y = a
        return x**2 + y**2

    def dot(self, a, b):
        x1, y1 = a
        x2, y2 = b
        return x1*x2 + y1*y2

    def cross(self, a, b):
        x1, y1 = a
        x2, y2 = b
        return x1*y2 - y1*x2

    def project(self, seg, p):
        """ 線分segに対する点pの射影 """
        p1, p2 = seg
        base = self.sub(p2, p1)
        r = self.dot(self.sub(p, p1), base) / self.norm(base)
        return self.add(p1, self.mul(base, r))

    def reflect(self, seg, p):
        """ 線分segを対称軸とした点pの線対称の点 """
        return self.add(p, self.mul(self.sub(self.project(seg, p), p), 2))

    def ccw(self, p0, p1, p2):
        """ 線分p0,p1から線分p0,p2への回転方向 """
        a = self.sub(p1, p0)
        b = self.sub(p2, p0)
        # 反時計回り
        if self.cross(a, b) > self.EPS: return 1
        # 時計回り
        if self.cross(a, b) < -self.EPS: return -1
        # 直線上(p2 => p0 => p1)
        if self.dot(a, b) < -self.EPS: return 2
        # 直線上(p0 => p1 => p2)
        if self.norm(a) < self.norm(b): return -2
        # 直線上(p0 => p2 => p1)
        return 0

    def intersect(self, seg1, seg2):
        """ 線分seg1と線分seg2の交差判定 """
        p1, p2 = seg1
        p3, p4 = seg2
        return (
            self.ccw(p1, p2, p3) * self.ccw(p1, p2, p4) <= 0
            and self.ccw(p3, p4, p1) * self.ccw(p3, p4, p2) <= 0
        )

    def get_distance_LP(self, line, p):
        """ 直線lineと点pの距離 """
        p1, p2 = line
        return abs(self.cross(self.sub(p2, p1), self.sub(p, p1)) / self.abs(self.sub(p2, p1)))

    def get_distance_SP(self, seg, p):
        """ 線分segと点pの距離 """
        p1, p2 = seg
        if self.dot(self.sub(p2, p1), self.sub(p, p1)) < 0: return self.abs(self.sub(p, p1))
        if self.dot(self.sub(p1, p2), self.sub(p, p2)) < 0: return self.abs(self.sub(p, p2))
        return self.get_distance_LP(seg, p)

    def get_distance_SS(self, seg1, seg2):
        """ 線分seg1と線分seg2の距離 """
        p1, p2 = seg1
        p3, p4 = seg2
        if self.intersect(seg1, seg2): return 0
        return min(
            self.get_distance_SP(seg1, p3), self.get_distance_SP(seg1, p4),
            self.get_distance_SP(seg2, p1), self.get_distance_SP(seg2, p2),
        )

gm = Geometry()
for _ in range(INT()):
    x1, y1, x2, y2, x3, y3, x4, y4 = MAP()
    seg1 = ((x1, y1), (x2, y2))
    seg2 = ((x3, y3), (x4, y4))
    print(gm.get_distance_SS(seg1, seg2))

Submission status: Accepted

Solution code:
from itertools import starmap


def cross(a: complex, b: complex) -> float:
    return float(a.real * b.imag - a.imag * b.real)


def is_intersected(p0: complex, p1: complex, p2: complex, p3: complex) -> bool:
    max_x1, min_x1 = (p0.real, p1.real) if p0.real > p1.real else (p1.real, p0.real)
    max_x2, min_x2 = (p2.real, p3.real) if p2.real > p3.real else (p3.real, p2.real)
    if max_x1 < min_x2 or max_x2 < min_x1:
        return False
    max_y1, min_y1 = (p0.imag, p1.imag) if p0.imag > p1.imag else (p1.imag, p0.imag)
    max_y2, min_y2 = (p2.imag, p3.imag) if p2.imag > p3.imag else (p3.imag, p2.imag)
    if max_y1 < min_y2 or max_y2 < min_y1:
        return False

    return (cross(p1 - p0, p2 - p0) * cross(p1 - p0, p3 - p0) < 1e-6
            and cross(p3 - p2, p0 - p2) * cross(p3 - p2, p1 - p2) < 1e-6)


def point_to_segment(p0: complex, p1: complex, p2: complex) -> float:
    prod = (p1 - p0).conjugate() * (p2 - p0)
    if prod.real <= 1e-6:
        return abs(p2 - p0)
    l = abs(p1 - p0)  # noqa: E741
    d = prod.real / l
    if d >= l:
        return abs(p2 - p1)
    return abs(prod.imag) / l


if __name__ == "__main__":
    q = int(input())
    for _ in range(q):
        x_p0, y_p0, x_p1, y_p1, x_p2, y_p2, x_p3, y_p3 = map(lambda x: int(x),
                                                             input().split())
        p0 = complex(x_p0, y_p0)
        p1 = complex(x_p1, y_p1)
        p2 = complex(x_p2, y_p2)
        p3 = complex(x_p3, y_p3)

        if is_intersected(p0, p1, p2, p3):
            print(0)
            continue

        ans = min(starmap(point_to_segment,
                  ((p0, p1, p2), (p0, p1, p3), (p2, p3, p0), (p2, p3, p1))))
        print(ans)

Submission status: Accepted

Solution code:
EPS = 1e-4

#点と線分の距離
def PointSegmentDistance(point, begin, end):
	point, begin, end = point-begin, 0, end-begin
	point = (point / end) * abs(end)
	end = abs(end)
	if -EPS <= point.real <= abs(end):
		return abs(point.imag)
	else:
		return min(abs(point), abs(point - end))

#外積
def OuterProduct(one, two):
	tmp = one.conjugate() * two
	return tmp.imag

#内積
def InnerProduct(one, two):
	tmp = one.conjugate() * two
	return tmp.real

#点が線分上にあるか
def IsOnSegment(point, begin, end):
	if abs(OuterProduct(begin-point, end-point)) <= EPS and InnerProduct(begin-point, end-point) <= EPS:
		return True
	else:
		return False

#3点が反時計回りか
#一直線上のときの例外処理できていない→とりあえずF
def CCW(p, q, r):
	one, two = q-p, r-q
	if OuterProduct(one, two) > -EPS:
		return True
	else:
		return False

#線分どうし交叉
def Intersect_SS(b1, e1, b2, e2):
	if IsOnSegment(b1, b2, e2) or IsOnSegment(e1, b2, e2) or IsOnSegment(b2, b1, e1) or IsOnSegment(e2, b1, e1):
		return True
	elif (CCW(b1, e1, b2) != CCW(b1, e1, e2)) and (CCW(b2, e2, b1) != CCW(b2, e2, e1)):
		return True
	else:
		return False

#点と線分の距離
def SegmentSegmentDistance(a, b, c, d):
	if Intersect_SS(a, b, c, d):
		return 0
	else:
		return min(PointSegmentDistance(a, c, d), PointSegmentDistance(b, c, d), PointSegmentDistance(c, a, b), PointSegmentDistance(d, a, b))

n = int(input())
for _ in range(n):
	pp = list(map(int, input().split()))
	p = [complex(pp[i], pp[i+1]) for i in range(0, 8, 2)]
	print(SegmentSegmentDistance(p[0], p[1], p[2], p[3]))

Submission status: Accepted

Solution code:
from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inp(): return int(input())
def inpl(): return list(map(int, input().split()))
def inpl_str(): return list(input().split())

###########################
#          幾何
###########################
def sgn(a):
    if a < -eps: return -1
    if a >  eps: return  1
    return 0

class Point:
    def __init__(self,x,y):
        self.x = x
        self.y = y
        pass

    def tolist(self):
        return [self.x,self.y]

    def __add__(self,p):
        return Point(self.x+p.x, self.y+p.y)
    def __iadd__(self,p):
        return self + p

    def __sub__(self,p):
        return Point(self.x - p.x, self.y - p.y)
    def __isub__(self,p):
        return self - p

    def __truediv__(self,n):
        return Point(self.x/n, self.y/n)
    def __itruediv__(self,n):
        return self / n

    def __mul__(self,n):
        return Point(self.x*n, self.y*n)
    def __imul__(self,n):
        return self * n

    def __lt__(self,other):
        tmp = sgn(self.x - other.x)
        if tmp != 0:
            return tmp < 0
        else:
            return sgn(self.y - other.y) < 0

    def __eq__(self,other):
        return sgn(self.x - other.x) == 0 and sgn(self.y - other.y) == 0

    def abs(self):
        return math.sqrt(self.x**2+self.y**2)

    def dot(self,p):
        return self.x * p.x + self.y*p.y

    def det(self,p):
        return self.x * p.y - self.y*p.x

    def arg(self,p):
        return math.atan2(y,x)

# 点の進行方向 a -> b -> c
def iSP(a,b,c):
    tmp = sgn((b-a).det(c-a))
    if tmp > 0:   return 1   # 左に曲がる場合
    elif tmp < 0: return -1  # 右に曲がる場合
    else: # まっすぐ
        if sgn((b-a).dot(c-a)) < 0: return -2 # c-a-b の順
        if sgn((a-b).dot(c-b)) < 0: return  2 # a-b-c の順
        return 0 # a-c-bの順

# ab,cd の直線交差
def isToleranceLine(a,b,c,d):
    if sgn((b-a).det(c-d)) != 0: return 1 # 交差する
    else:
        if sgn((b-a).det(c-a)) != 0: return 0 # 平行
        else: return -1 # 同一直線

# ab,cd の線分交差 重複，端点での交差もTrue
def isToleranceSegline(a,b,c,d):
    return sgn(iSP(a,b,c)*iSP(a,b,d))<=0 and sgn(iSP(c,d,a)*iSP(c,d,b)) <= 0

# 直線ab と 直線cd の交点 (存在する前提)
def Intersection(a,b,c,d):
    tmp1 = (b-a)*((c-a).det(d-c))
    tmp2 = (b-a).det(d-c)
    return a+(tmp1/tmp2)

# 直線ab と 点c の距離
def DistanceLineToPoint(a,b,c):
    return abs(((c-a).det(b-a))/((b-a).abs()))

# 線分ab と 点c の距離
def DistanceSeglineToPoint(a,b,c):
    if sgn((b-a).dot(c-a)) < 0: # <cab が鈍角
        return (c-a).abs()
    if sgn((a-b).dot(c-b)) < 0: # <cba が鈍角
        return (c-b).abs()
    return DistanceLineToPoint(a,b,c)

# 直線ab への 点c からの垂線の足
def Vfoot(a,b,c):
    d = c + Point((b-a).y,-(b-a).x)
    return Intersection(a,b,c,d)

# 多角形の面積
def PolygonArea(Plist):
    Plist = ConvexHull(Plist)
    L = len(Plist)
    S = 0
    for i in range(L):
        tmpS = (Plist[i-1].det(Plist[i]))/2
        S += tmpS
    return S

# 多角形の重心
def PolygonG(Plist):
    Plist = ConvexHull(Plist)
    L = len(Plist)
    S = 0
    G = Point(0,0)
    for i in range(L):
        tmpS = (Plist[i-1].det(Plist[i]))/2
        S += tmpS
        G += (Plist[i-1]+Plist[i])/3*tmpS
    return G/S

# 凸法
def ConvexHull(Plist):
    Plist.sort()
    L = len(Plist)
    qu = deque([])
    quL = 0
    for p in Plist:
        while quL >= 2 and iSP(qu[quL-2],qu[quL-1],p) == 1:
            qu.pop()
            quL -= 1
        qu.append(p)
        quL += 1

    qd = deque([])
    qdL = 0
    for p in Plist:
        while qdL >= 2 and iSP(qd[qdL-2],qd[qdL-1],p) == -1:
            qd.pop()
            qdL -= 1
        qd.append(p)
        qdL += 1

    qd.pop()
    qu.popleft()
    hidari = list(qd) + list(reversed(qu)) # 左端開始，左回りPlist
    return hidari

N = int(input())
for _ in range(N):
    x0,y0,x1,y1,x2,y2,x3,y3 = inpl()
    p0 = Point(x0,y0)
    p1 = Point(x1,y1)
    p2 = Point(x2,y2)
    p3 = Point(x3,y3)
    if isToleranceSegline(p0,p1,p2,p3):
        print(0)
    else:
        print(min(DistanceSeglineToPoint(p0,p1,p2),\
                  DistanceSeglineToPoint(p0,p1,p3),\
                  DistanceSeglineToPoint(p2,p3,p0),\
                  DistanceSeglineToPoint(p2,p3,p1)))

Submission status: Accepted

Solution code:
import math


class Vector2():
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __add__(self, v):
        return Vector2(self.x+v.x, self.y+v.y)

    def __sub__(self, v):
        return Vector2(self.x-v.x, self.y-v.y)

    def __mul__(self, v):
        return Vector2(self.x*v, self.y*v)

    def __truediv__(self, v):
        return Vector2(self.x/v, self.y/v)

    def __abs__(self):
        return math.sqrt(float(self.x*self.x+self.y*self.y))

    def dot(self, v):
        return self.x*v.x+self.y*v.y

    def cross(self, v):
        return self.x*v.y-self.y*v.x

    def norm(self):
        d = abs(self)
        return Vector2(self.x/d, self.y/d)


def distanceLP(v1, v2, p):
    '''
    v1 -> v2の直線とpとの距離
    '''
    return abs((v2-v1).cross(p-v1))/abs(v2-v1)


def distanceSP(v1, v2, p):
    '''
    v1 -> v2の線分とpとの距離
    '''
    if (v2-v1).dot(p-v1) < 0.0:
        return abs(p-v1)
    if (v1-v2).dot(p-v2) < 0.0:
        return abs(p-v2)
    return distanceLP(v1, v2, p)


def intersect(p1, p2, p3, p4):
    '''
    p1p2とp3p4の交差判定
    '''
    t1 = (p1.x-p2.x)*(p3.y-p1.y)+(p1.y-p2.y)*(p1.x-p3.x)
    t2 = (p1.x-p2.x)*(p4.y-p1.y)+(p1.y-p2.y)*(p1.x-p4.x)
    t3 = (p3.x-p4.x)*(p1.y-p3.y)+(p3.y-p4.y)*(p3.x-p1.x)
    t4 = (p3.x-p4.x)*(p2.y-p3.y)+(p3.y-p4.y)*(p3.x-p2.x)
    return (t1*t2) < 0.0 and (t3*t4) < 0.0


def distance(a1, a2, b1, b2):
    '''
    線分a1a2とb1b2の距離
    '''
    if intersect(a1, a2, b1, b2):
        return 0.0
    return min([
        min([distanceSP(a1, a2, b1), distanceSP(a1, a2, b2)]),
        min([distanceSP(b1, b2, a1), distanceSP(b1, b2, a2)])
    ])


q = int(input())
for i in range(q):
    x0, y0, x1, y1, x2, y2, x3, y3 = map(int, input().split())
    p0 = Vector2(x0, y0)
    p1 = Vector2(x1, y1)
    p2 = Vector2(x2, y2)
    p3 = Vector2(x3, y3)
    s1 = p1-p0
    s2 = p3-p2
    print(f"{distance(p0, p1, p2, p3):.10f}")

Submission status: Accepted

Solution code:
import math


def dot(ux, uy, vx, vy):
    return ux*vx + uy*vy


def cross(ux, uy, vx, vy):
    return ux*vy - uy*vx


def dist_to_segment(x, y, ax, ay, bx, by):
    if dot(x - ax, y - ay, bx - ax, by - ay) < 0:
        return math.hypot(x - ax, y - ay)
    if dot(x - bx, y - by, ax - bx, ay - by) < 0:
        return math.hypot(x - bx, y - by)
    c = abs(cross(bx - ax, by - ay, x - ax, y - ay))
    return c / math.hypot(bx - ax, by - ay)


q = int(input())

for _ in range(q):
    x0, y0, x1, y1, x2, y2, x3, y3 = map(int, input().split())

    c1 = cross(x1 - x0, y1 - y0, x2 - x0, y2 - y0)
    c2 = cross(x1 - x0, y1 - y0, x3 - x0, y3 - y0)
    c3 = cross(x3 - x2, y3 - y2, x0 - x2, y0 - y2)
    c4 = cross(x3 - x2, y3 - y2, x1 - x2, y1 - y2)

    if c1*c2 < 0 and c3*c4 < 0:
        d = 0.0
    else:
        d = dist_to_segment(x2, y2, x0, y0, x1, y1)
        d = min(d, dist_to_segment(x3, y3, x0, y0, x1, y1))
        d = min(d, dist_to_segment(x0, y0, x2, y2, x3, y3))
        d = min(d, dist_to_segment(x1, y1, x2, y2, x3, y3))

    print('{:.10f}'.format(d))

Submission status: Accepted

Solution code:
#!/usr/bin/env python3
# CGL_2_D: Segments/Lines - Distance

from math import sqrt


class Segment:
    def __init__(self, p0, p1):
        self.end_points = (p0, p1)

    def another(self, p):
        if p == self.end_points[0]:
            return self.end_points[1]
        else:
            return self.end_points[0]

    def distance(self, other):
        def _distance(p, seg):
            p0 = seg._closest_point(p)
            p1 = seg.another(p0)
            x, y = p
            x0, y0 = p0
            x1, y1 = p1
            vp = (x-x0, y-y0)
            vseg = (x1-x0, y1-y0)
            if dot(vp, vseg) <= 0:
                return length(vp)
            else:
                x, y = vp
                return length(projection(vp, orthogonal(vseg)))

        if self.intersect(other):
            return 0.0

        dists = []
        for p0 in self.end_points:
            dists.append(_distance(p0, other))
        for p1 in other.end_points:
            dists.append(_distance(p1, self))

        return min(dists)

    def intersect(self, other):
        p0, p1 = self.end_points
        p2, p3 = other.end_points

        if convex(p0, p2, p1, p3):
            return True
        else:
            if (p0 in other or p1 in other
                    or p2 in self or p3 in self):
                return True

        return False

    def _closest_point(self, p):
        p0, p1 = self.end_points
        x, y = p
        x0, y0 = p0
        x1, y1 = p1
        if length((x0-x, y0-y)) < length((x1-x, y1-y)):
            return p0
        else:
            return p1

    def __contains__(self, p):
        p0, p1 = self.end_points
        x0, y0 = p0
        x1, y1 = p1
        x, y = p
        v = (x1-x0, y1-y0)
        v0 = (x-x0, y-y0)
        v1 = (x-x1, y-y1)
        if dot(orthogonal(v0), v1) == 0:
            if abs(length(v0) + length(v1) - length(v)) < 1e-10:
                return True
        return False


def dot(v1, v2):
    x1, y1 = v1
    x2, y2 = v2
    return x1 * x2 + y1 * y2


def orthogonal(v):
    x, y = v
    return -y, x


def length(v):
    x, y = v
    return sqrt(x**2 + y**2)


def projection(p, v):
    x, y = v
    r = dot(p, v) / dot(v, v)
    return (x*r, y*r)


def convex(p0, p1, p2, p3):
    ret = []
    for pa, pb, pc in zip([p0, p1, p2, p3],
                          [p1, p2, p3, p0],
                          [p2, p3, p0, p1]):
        xa, ya = pa
        xb, yb = pb
        xc, yc = pc
        v1 = (xb - xa, yb - ya)
        v2 = (xc - xb, yc - yb)
        ret.append(dot(orthogonal(v1), v2))

    return all([d > 0 for d in ret]) or all([d < 0 for d in ret])


def run():
    q = int(input())

    for _ in range(q):
        x0, y0, x1, y1, x2, y2, x3, y3 = [int(i) for i in input().split()]

        s0 = Segment((x0, y0), (x1, y1))
        s1 = Segment((x2, y2), (x3, y3))

        print("{:.10f}".format(s0.distance(s1)))


if __name__ == '__main__':
    run()