Problem:
Closest Pair For given n points in metric space, find the distance of the closest points. Input  n  x 0  y 0  x 1  y 1 : x n-1  y n-1  The first integer n is the number of points. In the following n lines, the coordinate of the i -th point is given by two real numbers x i and y i . Each value is a real number with at most 6 digits after the decimal point. Output Print the distance in a line. The output values should be in a decimal fraction with an error less than 0.000001. Constraints  2 ≤ n ≤ 100,000  -100 ≤ x , y ≤ 100  Sample Input 1 2
0.0 0.0
1.0 0.0 Sample Output 1 1.000000 Sample Input 2 3
0.0 0.0
2.0 0.0
1.0 1.0 Sample Output 2 1.41421356237

Solution (Python):
import cmath
import itertools
import math
import os
import sys
from collections import defaultdict

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

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

PI = cmath.pi
TAU = cmath.pi * 2
EPS = 1e-10


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

    
    CCW_COUNTER_CLOCKWISE = 1
    
    CCW_CLOCKWISE = -1
    
    CCW_ONLINE_BACK = 2
    
    CCW_ONLINE_FRONT = -2
    
    CCW_ON_SEGMENT = 0

    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)

    @staticmethod
    def ccw(a, b, c):
        """
        線分 ab に対する c の位置
        線分上にあるか判定するだけなら on_segment とかのが速い
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_1_C&lang=ja
        :param Point a:
        :param Point b:
        :param Point c:
        """
        b = b - a
        c = c - a
        det = b.det(c)
        if det > EPS:
            return Point.CCW_COUNTER_CLOCKWISE
        if det < -EPS:
            return Point.CCW_CLOCKWISE
        if b.dot(c) < -EPS:
            return Point.CCW_ONLINE_BACK
        if c.norm() - b.norm() > EPS:
            return Point.CCW_ONLINE_FRONT
        return Point.CCW_ON_SEGMENT

    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 norm(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 に向いてる状態から q まで反時計回りに回転するときの角度
        -pi <= ret <= pi
        :param Point p:
        :param Point q:
        :rtype: float
        """
        return (cmath.phase(q.c - self.c) - cmath.phase(p.c - self.c) + PI) % TAU - PI

    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
        
        r = (self - p).dot(diff_q) / abs(diff_q)
        
        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
        """
        
        r = abs(self - p)
        
        angle = p.angle(q, self)
        
        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
        
        
        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:
        """
        
        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:
        """
        
        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_C&lang=ja
        :param Line 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:
            
            return None
        x = (b1 * c2 - b2 * c1) / det
        y = (a2 * c1 - a1 * c2) / det
        return Point.from_rect(x, y)

    def dist(self, p):
        """
        他の点との最短距離
        :param Point p:
        """
        raise NotImplementedError()

    def has_point(self, p):
        """
        p が直線上に乗っているかどうか
        :param Point p:
        """
        return abs(self.a * p.x + self.b * p.y + self.c) < EPS


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 phase(self):
        """
        p1 を原点としたときの p2 の角度
        """
        return cmath.phase(self.p2 - self.p1)

    def is_parallel_to(self, s):
        """
        平行かどうか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_A&lang=ja
        :param Segment s:
        :return:
        """
        
        return abs((self.p1 - self.p2).det(s.p1 - s.p2)) < EPS

    def is_orthogonal_to(self, s):
        """
        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 Segment s:
        :return:
        """
        
        return abs((self.p1 - self.p2).dot(s.p1 - s.p2)) < EPS

    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
        """
        if self.is_parallel_to(s):
            
            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:
            
            det_upper = EPS if allow_side else -EPS
            ok = True
            
            ok &= (self.p2 - self.p1).det(s.p1 - self.p1) * (self.p2 - self.p1).det(s.p2 - self.p1) < det_upper
            
            ok &= (s.p2 - s.p1).det(self.p1 - s.p1) * (s.p2 - s.p1).det(self.p2 - s.p1) < det_upper
            return ok

    def closest_point(self, p):
        """
        線分上の、p に最も近い点
        :param Point p:
        """
        
        d = (p - self.p1).dot(self.p2 - self.p1) / self.norm()
        
        if d < EPS:
            return self.p1
        
        if -EPS < d - self.norm():
            return self.p2
        
        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
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_D&lang=ja
        :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),
        )

    def has_point(self, p, allow_side=True):
        """
        p が線分上に乗っているかどうか
        :param Point p:
        :param allow_side: 端っこでギリギリ触れているのを許容するか
        """
        return p.on_segment(self.p1, self.p2, allow_side=allow_side)


class Polygon:
    """
    2次元空間上の多角形
    """

    def __init__(self, points):
        """
        :param list of Point points:
        """
        self.points = points

    def iter2(self):
        """
        隣り合う2点を順に返すイテレータ
        :rtype: typing.Iterator[(Point, Point)]
        """
        return zip(self.points, self.points[1:] + self.points[:1])

    def iter3(self):
        """
        隣り合う3点を順に返すイテレータ
        :rtype: typing.Iterator[(Point, Point, Point)]
        """
        return zip(self.points,
                   self.points[1:] + self.points[:1],
                   self.points[2:] + self.points[:2])

    def area(self):
        """
        面積
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_3_A&lang=ja
        """
        
        dets = []
        for p, q in self.iter2():
            dets.append(p.det(q))
        return abs(math.fsum(dets)) / 2

    def is_convex(self, allow_straight=False, allow_collapsed=False):
        """
        凸多角形かどうか
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_3_B&lang=ja
        :param allow_straight: 3点がまっすぐ並んでるのを許容するかどうか
        :param allow_collapsed: 面積がゼロの場合を許容するか
        """
        ccw = []
        for a, b, c in self.iter3():
            ccw.append(Point.ccw(a, b, c))
        ccw = set(ccw)
        if len(ccw) == 1:
            if ccw == {Point.CCW_CLOCKWISE}:
                return True
            if ccw == {Point.CCW_COUNTER_CLOCKWISE}:
                return True
        if allow_straight and len(ccw) == 2:
            if ccw == {Point.CCW_ONLINE_FRONT, Point.CCW_CLOCKWISE}:
                return True
            if ccw == {Point.CCW_ONLINE_FRONT, Point.CCW_COUNTER_CLOCKWISE}:
                return True
        if allow_collapsed and len(ccw) == 3:
            return ccw == {Point.CCW_ONLINE_FRONT, Point.CCW_ONLINE_BACK, Point.CCW_ON_SEGMENT}
        return False

    def has_point_on_edge(self, p):
        """
        指定した点が辺上にあるか
        :param Point p:
        :rtype: bool
        """
        for a, b in self.iter2():
            if p.on_segment(a, b):
                return True
        return False

    def contains(self, p, allow_on_edge=True):
        """
        指定した点を含むか
        Winding Number Algorithm
        https://www.nttpc.co.jp/technology/number_algorithm.html
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_3_C&lang=ja
        :param Point p:
        :param bool allow_on_edge: 辺上の点を許容するか
        """
        angles = []
        for a, b in self.iter2():
            if p.on_segment(a, b):
                return allow_on_edge
            angles.append(p.angle(a, b))
        
        return abs(math.fsum(angles)) > EPS

    @staticmethod
    def convex_hull(points, allow_straight=False):
        """
        凸包。x が最も小さい点のうち y が最も小さい点から反時計回り。
        Graham Scan O(N log N)
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_A&lang=ja
        :param list of Point points:
        :param allow_straight: 3点がまっすぐ並んでるのを許容するかどうか
        :rtype: list of Point
        """
        points = points[:]
        points.sort(key=lambda p: (p.x, p.y))

        
        det_lower = -EPS if allow_straight else EPS

        sz = 0
        
        ret = [None] * (len(points) * 2)
        for p in points:
            while sz > 1 and (ret[sz - 1] - ret[sz - 2]).det(p - ret[sz - 1]) < det_lower:
                sz -= 1
            ret[sz] = p
            sz += 1
        floor = sz
        for p in reversed(points[:-1]):
            while sz > floor and (ret[sz - 1] - ret[sz - 2]).det(p - ret[sz - 1]) < det_lower:
                sz -= 1
            ret[sz] = p
            sz += 1
        ret = ret[:sz - 1]

        if allow_straight and len(ret) > len(points):
            
            ret = points
        return ret

    @staticmethod
    def diameter(points):
        """
        直径
        凸包構築 O(N log N) + カリパー法 O(N)
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_B&lang=ja
        :param list of Point points:
        """
        
        points = Polygon.convex_hull(points, allow_straight=False)
        if len(points) == 1:
            return 0.0
        if len(points) == 2:
            return abs(points[0] - points[1])

        
        si = points.index(min(points, key=lambda p: (p.x, p.y)))
        sj = points.index(max(points, key=lambda p: (p.x, p.y)))
        n = len(points)

        ret = 0.0
        
        i, j = si, sj
        while i != sj or j != si:
            ret = max(ret, abs(points[i] - points[j]))
            ni = (i + 1) % n
            nj = (j + 1) % n
            
            if (points[ni] - points[i]).det(points[nj] - points[j]) > 0:
                j = nj
            else:
                i = ni
        return ret

    def convex_cut_by_line(self, line_p1, line_p2):
        """
        凸多角形を直線 line_p1-line_p2 でカットする。
        凸じゃないといけません
        Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_C&lang=ja
        :param line_p1:
        :param line_p2:
        :return: (line_p1-line_p2 の左側の多角形, line_p1-line_p2 の右側の多角形)
        :rtype: (Polygon|None, Polygon|None)
        """
        n = len(self.points)
        line = Line.from_segment(line_p1, line_p2)
        
        on_line_points = []
        for i, p in enumerate(self.points):
            if line.has_point(p):
                on_line_points.append(i)

        
        has_on_line_edge = False
        if len(on_line_points) >= 3:
            has_on_line_edge = True
        elif len(on_line_points) == 2:
            
            has_on_line_edge = abs(on_line_points[0] - on_line_points[1]) in [1, n - 1]
        
        if has_on_line_edge:
            for p in self.points:
                ccw = Point.ccw(line_p1, line_p2, p)
                if ccw == Point.CCW_COUNTER_CLOCKWISE:
                    return Polygon(self.points[:]), None
                if ccw == Point.CCW_CLOCKWISE:
                    return None, Polygon(self.points[:])

        ret_lefts = []
        ret_rights = []
        d = line_p2 - line_p1
        for p, q in self.iter2():
            det_p = d.det(p - line_p1)
            det_q = d.det(q - line_p1)
            if det_p > -EPS:
                ret_lefts.append(p)
            if det_p < EPS:
                ret_rights.append(p)
            
            if det_p * det_q < -EPS:
                intersection = line.intersection_point(Line.from_segment(p, q))
                ret_lefts.append(intersection)
                ret_rights.append(intersection)

        
        l = Polygon(ret_lefts) if len(ret_lefts) > 1 else None
        r = Polygon(ret_rights) if len(ret_rights) > 1 else None
        return l, r


def closest_pair(points):
    """
    最近点対 O(N log N)
    Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_5_A&lang=ja
    :param list of Point points:
    :rtype: (float, (Point, Point))
    :return: (距離, 点対)
    """
    assert len(points) >= 2

    def _rec(xsorted):
        """
        :param list of Point xsorted:
        :rtype: (float, (Point, Point))
        """
        n = len(xsorted)
        if n <= 2:
            return xsorted[0].dist(xsorted[1]), (xsorted[0], xsorted[1])
        if n <= 3:
            
            d = INF
            pair = None
            for p, q in itertools.combinations(xsorted, r=2):
                if p.dist(q) < d:
                    d = p.dist(q)
                    pair = p, q
            return d, pair

        
        
        ld, lp = _rec(xsorted[:n // 2])
        rd, rp = _rec(xsorted[n // 2:])
        if ld <= rd:
            d = ld
            ret_pair = lp
        else:
            d = rd
            ret_pair = rp

        mid_x = xsorted[n // 2].x
        
        mid_points = []
        for p in xsorted:
            
            if abs(p.x - mid_x) - d < -EPS:
                mid_points.append(p)

        
        mid_points.sort(key=lambda p: p.y)
        mid_n = len(mid_points)
        for i in range(mid_n - 1):
            j = i + 1
            p = mid_points[i]
            q = mid_points[j]
            
            while (q.y - p.y) - d < -EPS:
                pq_d = p.dist(q)
                if pq_d < d:
                    d = pq_d
                    ret_pair = p, q
                j += 1
                if j >= mid_n:
                    break
                q = mid_points[j]
        return d, ret_pair

    return _rec(list(sorted(points, key=lambda p: p.x)))


def closest_pair_randomized(points):
    """
    最近点対 乱択版 O(N)
    グリッドの管理が dict だから定数倍気になる
    http://ir5.hatenablog.com/entry/20131221/1387557630
    Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_5_A&lang=ja
    :param list of Point points:
    :rtype: (float, (Point, Point))
    :return: (距離, 点対)
    """
    n = len(points)
    assert n >= 2
    if n == 2:
        return points[0].dist(points[1]), (points[0], points[1])

    
    import random
    points = points[:]
    random.shuffle(points)

    DELTA_XY = list(itertools.product([-1, 0, 1], repeat=2))
    grid = defaultdict(list)
    delta = INF
    dist = points[0].dist(points[1])
    ret_pair = points[0], points[1]
    for i in range(2, n):
        if delta < EPS:
            return 0.0, ret_pair
        
        
        if dist - delta < -EPS:
            delta = dist
            grid = defaultdict(list)
            for a in points[:i]:
                grid[a.x // delta, a.y // delta].append(a)
        else:
            p = points[i - 1]
            grid[p.x // delta, p.y // delta].append(p)

        p = points[i]
        dist = delta
        grid_x = p.x // delta
        grid_y = p.y // delta
        
        for dx, dy in DELTA_XY:
            for q in grid[grid_x + dx, grid_y + dy]:
                d = p.dist(q)
                
                if d - dist < -EPS:
                    dist = d
                    ret_pair = p, q
    return min(delta, dist), ret_pair


def closest_pair_randomized2(points):
    """
    最近点対 乱択版 O(N)
    グリッドの管理が dict だから定数倍気になる
    http://ir5.hatenablog.com/entry/20131221/1387557630
    Verify: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_5_A&lang=ja
    :param list of Point points:
    :rtype: (float, (Point, Point))
    :return: (距離, 点対)
    """
    n = len(points)
    assert n >= 2
    if n == 2:
        return points[0].dist(points[1]), (points[0], points[1])

    
    import random

    
    DIM = 2
    DELTA_XY = list(itertools.product([-1, 0, 1], repeat=2))

    all_points = points
    dist = points[0].dist(points[1])
    while points:
        next_points = []
        pi = random.choice(range(len(points)))
        p = points[pi]
        d = INF
        for qi, q in enumerate(points):
            if pi == qi:
                continue
            d = min(d, p.dist(q))
        
        width = d / (4 * DIM)
        grid = defaultdict(list)
        for p in points:
            grid[p.x // width, p.y // width].append(p)
        for p in points:
            grid_x = p.x // width
            grid_y = p.y // width
            cnt = 0
            for dx, dy in DELTA_XY:
                cnt += len(grid[grid_x + dx, grid_y + y])
            if cnt >= 2:
                next_points.append(p)

        dist = d
        points = next_points

    width = dist
    grid = defaultdict(list)
    for p in all_points:
        grid[p.x // width, p.y // width].append(p)
    ret = INF
    for p in all_points:
        grid_x = p.x // width
        grid_y = p.y // width
        
        for dx, dy in DELTA_XY:
            for q in grid[grid_x + dx, grid_y + dy]:
                if p == q:
                    
                    continue
                d = p.dist(q)
                
                if d - ret < -EPS:
                    ret = d
                    ret_pair = p, q
    return ret, ret_pair


N = int(sys.stdin.buffer.readline())
XY = [list(map(float, sys.stdin.buffer.readline().split())) for _ in range(N)]

points = []
for x, y in XY:
    points.append(Point(complex(x, y)))
d, (p, q) = closest_pair_randomized2(points)
print('{:.10f}'.format(d))

Solution (Python):

"""
Closest Pair
http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_5_A&lang=ja
TLE
"""
import sys


from collections import deque
def closest_pair(points):
    return find_closest(sorted(points)) ** 0.5

def find_closest(points):
    n = len(points)
    if n <= 1:
        return float('inf')
    m = n // 2
    x = points[m][0]
    d = min(find_closest(points[:m]),  find_closest(points[m:]))
    points.sort(key=lambda p:p[1])
    b = deque()
    for p in points:
        if (p[0] - x)**2 < d:
            for q in b:
                dx = p[0] - q[0]
                dy = p[1] - q[1]
                if dy**2 >= d:
                    break
                if (dx**2 + dy**2) < d:
                    d = (dx**2 + dy**2)
            b.appendleft(p)
    return d


def main(args):
    n = int(input())
    points = []
    for _ in range(n):
        x, y = map(float, input().split())
        points.append((x, y))
    ans = closest_pair(sorted(points))
    print('{:.10f}'.format(ans))


if __name__ == '__main__':
    main(sys.argv[1:])

Solution (Python):
from operator import itemgetter
from math import sqrt
from typing import List, Tuple


def distance(p: Tuple[float, float], q: Tuple[float, float]) -> float:
    return sqrt((p[0] - q[0]) ** 2 + (p[1] - q[1]) ** 2)


def closest_distance(points: List[Tuple[float, float]]) -> float:
    def split(i: int, j: int) -> float:
        if j - i < 2:
            return float('INF')
        mid = (i + j) // 2
        d = min(split(i, mid), split(mid, j))
        lv, rv = points[mid][0] - d, points[mid][0] + d
        return merge(sorted([p for p in points[i:j]
                             if lv <= p[0] <= rv], key=itemgetter(1)), d)

    def merge(_points: List[Tuple[float, float]], d: float) -> float:
        n = len(_points)
        for i in range(n - 1):
            for j in range(i + 1, n):
                if d < _points[j][1] - _points[i][1]:
                    break
                d = min(d, distance(_points[i], _points[j]))
        return d

    points.sort(key=itemgetter(0, 1))
    return split(0, len(points))


if __name__ == '__main__':
    n = int(input())
    points = [tuple(map(float, input().split())) for _ in range(n)]
    print("{:.6f}".format(closest_distance(points)))

Solution (Python):


import sys
from operator import itemgetter
from math import hypot
from bisect import bisect_left, bisect_right

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N=INT()
A=[]
for i in range(N):
    x,y=map(float, input().split())
    A.append((i, x, y))


Ax=sorted(A, key=itemgetter(1))
Ay=sorted(A, key=itemgetter(2))

def find_min(li):
    n=len(li)
    mn=INF
    for i in range(n):
        for j in range(i+1, n):
            _,x1,y1=li[i]
            _,x2,y2=li[j]
            mn=min(mn, hypot(x1-x2, y1-y2))
    return mn


def find_min2(mn, li1, li2):
    
    li2b=[y for i, x, y in li2]
    mn=INF
    for i1, x1, y1 in li1:
        s=bisect_left(li2b, y1-mn)
        t=bisect_right(li2b, y1+mn)
        
        for i in range(s, t):
            i2,x2,y2=li2[i]
            
            if i1==i2: continue
            mn=min(mn, hypot(x1-x2, y1-y2))
    return mn


def find_min3(mn, li1, li2):
    li2b=[x for i, x, y in li2]
    mn=INF
    for i1, x1, y1 in li1:
        s=bisect_left(li2b, x1-mn)
        t=bisect_right(li2b, x1+mn)
        for i in range(s, t):
            i2,x2,y2=li2[i]
            if i1==i2: continue
            mn=min(mn, hypot(x1-x2, y1-y2))
    return mn

def rec(lix, liy, d):
    
    if len(lix)<=3:
        return find_min(lix)
    
    if d%2==0:
        lix2=lix[:len(lix)//2]
        lix3=lix[len(lix)//2:]
        xset={x[0] for x in lix2}
        liy2=[]
        liy3=[]
        
        for i, x, y in liy:
            if i in xset:
                liy2.append((i, x, y))
            else:
                liy3.append((i, x, y))
        
        mn=min(rec(lix2, liy2, d^1), rec(lix3, liy3, d^1))
        
        midx=(lix2[-1][1]+lix3[0][1])/2
        borders1=[]
        borders2=[]
        for i in range(len(lix)):
            if midx-mn<=lix[i][1]<=midx+mn:
                borders1.append(lix[i])
            if midx-mn<=liy[i][1]<=midx+mn:
                borders2.append(liy[i]) 
        mn=min(mn, find_min2(mn, borders1, borders2))
        return mn
    
    else:
        liy2=liy[:len(liy)//2]
        liy3=liy[len(liy)//2:]
        yset={y[0] for y in liy2}
        lix2=[]
        lix3=[]
        for i, x, y in lix:
            if i in yset:
                lix2.append((i, x, y))
            else:
                lix3.append((i, x, y))
        mn=min(rec(lix2, liy2, d^1), rec(lix3, liy3, d^1))
        midy=(liy2[-1][2]+liy3[0][2])/2
        borders1=[]
        borders2=[]
        for i in range(len(liy)):
            if midy-mn<=liy[i][1]<=midy+mn:
                borders1.append(liy[i])
            if midy-mn<=lix[i][1]<=midy+mn:
                borders2.append(lix[i])
        mn=min(mn, find_min3(mn, borders1, borders2))
        return mn

print('{:.10f}'.format(rec(Ax, Ay, 0)))

Solution (Python):
import math
from itertools import combinations
from operator import itemgetter

pts = []
line = input()
n = int(line)
for _ in range(0, n):
    line = input()
    x, y = list(map(float, line.split()))
    pts += [[x, y]]

def dist(p, q):
    x1, y1 = p
    x2, y2 = q
    return (x1 - x2)**2 + (y1 - y2)**2

def solve(p, axis):
    n = len(p)
    if n <= 3:
        d = 100000
        q1 = q2 = []
        for p1, p2 in list(combinations(p, 2)):
            d = min(d, dist(p1, p2))
        return d

    mid = n // 2
    px, py = zip(*p)
    axis1 = 2 * len(set(px)) <= n
    axis2 = not axis1
    if axis1 != axis:
        p.sort(key = itemgetter(axis1))
    
    xy0 = p[mid][axis1]
    left = p[:mid]
    right = p[mid:]
    d = min(solve(left, axis1), solve(right, axis1))
    rd = math.sqrt(d)
    
    Q = []
    for pp in left[::-1]:
        if pp[axis1] < xy0 - rd:
            break
        Q.append(pp)
    for pp in right:
        if pp[axis1] > xy0 + rd:
            break
        Q.append(pp)
    Q.sort(key = itemgetter(axis2))
    for i, p1 in enumerate(Q):
        dd = p1[axis2] + rd
        for p2 in Q[i + 1:]:
            if p2[axis2] > dd:
                break
            norm = dist(p1, p2)
            if d > norm:
                d = norm
    return d

pts.sort(key = itemgetter(0))
ans = solve(pts, 0)
print('%.16f' % math.sqrt(ans))

Solution (Python):
import sys
from operator import itemgetter
from math import hypot
from itertools import takewhile, chain, combinations

def ntp(A: list, axis: int = -1):
    length = len(A)
    if length <= 4:
        return min([hypot(x1 - x2, y1 - y2) for (x1, y1), (x2, y2) in combinations(A, 2)])
    
    x_types = len(set(x for x, _ in A))
    axis1 = 2*x_types <= length
    axis2 = not axis1
    mid_idx = length//2
    
    if axis1 != axis:
        A.sort(key = itemgetter(axis1))
    Al, Ar = A[:mid_idx], A[mid_idx:]
    median = A[mid_idx][axis1]
    
    tmd = min(ntp(Al, axis1), ntp(Ar, axis1))
    
    midA = [p for p in chain(takewhile(lambda t: median - tmd < t[axis1], Al[::-1]),\
                             takewhile(lambda t: median + tmd > t[axis1], Ar))]
    midA.sort(key = itemgetter(axis2))
    for i, (x1, y1) in enumerate(midA):
        ub = (x1, y1)[axis2] + tmd
        for x2, y2 in takewhile(lambda t: t[axis2] < ub, midA[i+1:]):
            tmd = min(tmd, hypot(x1 - x2, y1 - y2))
    
    return tmd
n = int(sys.stdin.readline())
Points = [tuple(map(float, sys.stdin.readline().split())) for _ in [0]*n] 
print('{:.10f}'.format(ntp(Points)))