Problem:
Closest Pair

For given n points in metric space, find the distance of the closest points.

Input

n
x0 y0
x1 y1
:
xn-1 yn-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 xi and yi. 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 in Rust (judge verdict: Accepted)

/**
*  _           _                 __                            _   _ _   _                                 _                    _                  _
* | |         | |               / /                           | | (_) | (_)                               | |                  (_)                | |
* | |__   __ _| |_ ___   ___   / /__ ___  _ __ ___  _ __   ___| |_ _| |_ ___   _____ ______ _ __ _   _ ___| |_ ______ ___ _ __  _ _ __  _ __   ___| |_ ___
* | '_ \ / _` | __/ _ \ / _ \ / / __/ _ \| '_ ` _ \| '_ \ / _ \ __| | __| \ \ / / _ \______| '__| | | / __| __|______/ __| '_ \| | '_ \| '_ \ / _ \ __/ __|
* | | | | (_| | || (_) | (_) / / (_| (_) | | | | | | |_) |  __/ |_| | |_| |\ V /  __/      | |  | |_| \__ \ |_       \__ \ | | | | |_) | |_) |  __/ |_\__ \
* |_| |_|\__,_|\__\___/ \___/_/ \___\___/|_| |_| |_| .__/ \___|\__|_|\__|_| \_/ \___|      |_|   \__,_|___/\__|      |___/_| |_|_| .__/| .__/ \___|\__|___/
*                                                  | |                                                                           | |   | |
*                                                  |_|                                                                           |_|   |_|
*
* https://github.com/hatoo/competitive-rust-snippets
*/
#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};
mod util {
    use std::io::{stdin, stdout, BufWriter, StdoutLock};
    use std::str::FromStr;
    use std::fmt::Debug;
    #[allow(dead_code)]
    pub fn line() -> String {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.trim().to_string()
    }
    #[allow(dead_code)]
    pub fn chars() -> Vec<char> {
        line().chars().collect()
    }
    #[allow(dead_code)]
    pub fn gets<T: FromStr>() -> Vec<T>
    where
        <T as FromStr>::Err: Debug,
    {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|t| t.parse().unwrap())
            .collect()
    }
    #[allow(dead_code)]
    pub fn with_bufwriter<F: FnOnce(BufWriter<StdoutLock>) -> ()>(f: F) {
        let out = stdout();
        let writer = BufWriter::new(out.lock());
        f(writer)
    }
}
#[allow(unused_macros)]
macro_rules ! get { ( $ t : ty ) => { { let mut line : String = String :: new ( ) ; stdin ( ) . read_line ( & mut line ) . unwrap ( ) ; line . trim ( ) . parse ::<$ t > ( ) . unwrap ( ) } } ; ( $ ( $ t : ty ) ,* ) => { { let mut line : String = String :: new ( ) ; stdin ( ) . read_line ( & mut line ) . unwrap ( ) ; let mut iter = line . split_whitespace ( ) ; ( $ ( iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) , ) * ) } } ; ( $ t : ty ; $ n : expr ) => { ( 0 ..$ n ) . map ( | _ | get ! ( $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ ( $ t : ty ) ,*; $ n : expr ) => { ( 0 ..$ n ) . map ( | _ | get ! ( $ ( $ t ) ,* ) ) . collect ::< Vec < _ >> ( ) } ; ( $ t : ty ;; ) => { { let mut line : String = String :: new ( ) ; stdin ( ) . read_line ( & mut line ) . unwrap ( ) ; line . split_whitespace ( ) . map ( | t | t . parse ::<$ t > ( ) . unwrap ( ) ) . collect ::< Vec < _ >> ( ) } } ; ( $ t : ty ;; $ n : expr ) => { ( 0 ..$ n ) . map ( | _ | get ! ( $ t ;; ) ) . collect ::< Vec < _ >> ( ) } ; }
#[allow(unused_macros)]
macro_rules ! debug { ( $ ( $ a : expr ) ,* ) => { eprintln ! ( concat ! ( $ ( stringify ! ( $ a ) , " = {:?}, " ) ,* ) , $ ( $ a ) ,* ) ; } }
const BIG_STACK_SIZE: bool = false;
#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}

#[derive(PartialEq, PartialOrd)]
/// Implement Eq and Ord for a type which has only PartialEq and PartialOrd.
/// It is useful when sorting a Vec of f64
pub struct Total<T>(pub T);
impl<T: PartialEq> Eq for Total<T> {}
impl<T: PartialOrd> Ord for Total<T> {
    fn cmp(&self, other: &Total<T>) -> Ordering {
        self.0.partial_cmp(&other.0).unwrap()
    }
}

fn closest_pair(ps: &[(f64, f64)]) -> ((f64, f64), (f64, f64)) {
    fn d(p1: (f64, f64), p2: (f64, f64)) -> f64 {
        ((p1.0 - p2.0).powi(2) + (p1.1 - p2.1).powi(2)).sqrt()
    }

    fn rec(x_sort: &[(f64, f64)], y_sort: &[(f64, f64)]) -> ((f64, f64), (f64, f64)) {
        if x_sort.len() <= 3 {
            let mut min_d = std::f64::MAX;
            let mut pair = ((0.0, 0.0), (0.0, 0.0));
            for (i, &p1) in x_sort.iter().enumerate() {
                for (j, &p2) in x_sort.iter().enumerate() {
                    if i != j {
                        let dist = d(p1, p2);
                        if dist < min_d {
                            min_d = dist;
                            pair = (p1, p2);
                        }
                    }
                }
            }

            return pair;
        }

        let mid = x_sort.len() / 2;
        let pivot = x_sort[mid].0;

        let q_x = &x_sort[..mid];
        let r_x = &x_sort[mid..];

        let mut q_y = Vec::with_capacity(mid);
        let mut r_y = Vec::with_capacity(x_sort.len() - mid);

        for &(x, y) in y_sort {
            if x < pivot {
                q_y.push((x, y));
            } else {
                r_y.push((x, y));
            }
        }

        let pair1 = rec(q_x, &q_y);
        let pair2 = rec(r_x, &r_y);

        let w = d(pair1.0, pair1.1).min(d(pair2.0, pair2.1));
        let s: Vec<(f64, f64)> = y_sort
            .iter()
            .filter(|&&(x, _)| (pivot - x).abs() <= w)
            .cloned()
            .collect();

        let mut min_d = w;
        let mut pair = if d(pair1.0, pair1.1) < d(pair2.0, pair2.1) {
            pair1
        } else {
            pair2
        };

        for (i, &p1) in s.iter().enumerate() {
            for &p2 in s[i + 1..].iter().take(15) {
                let dist = d(p1, p2);
                if dist < min_d {
                    min_d = dist;
                    pair = (p1, p2);
                }
            }
        }
        pair
    }

    let mut x_sort = ps.to_vec();
    let mut y_sort = ps.to_vec();

    x_sort.sort_by_key(|p| Total(p.0));
    y_sort.sort_by_key(|p| Total(p.1));
    rec(&x_sort, &y_sort)
}

fn solve() {
    let n = get!(usize);
    let ps = get!(f64, f64; n);

    let ((a, b), (c, d)) = closest_pair(&ps);

    println!("{}", ((a - c).powi(2) + (b - d).powi(2)).sqrt());
}