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Challenge: Get Closest Number in an Array

Andy Zhao (he/him) on February 20, 2019

Given an array of numbers nums, and a given number given_num: nums = [100, 200, 400, 800, 1600, 3200, 6400, 128000] given_num = 900 Enter...

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Andrew Bone • Feb 21 '19 • Edited

Javascript:

Let's go for a JS one liner 😉

nums.sort((a, b) => Math.abs(given_num - a) - Math.abs(given_num - b))[0]

This causes the original array to have its order changed but I don't think that's against the rules 😅

bugb • Feb 21 '19 • Edited

I dont think use sort is good idea:
Let see:

[2,3,4,11].sort()

Andrew Bone • Feb 21 '19

By including a function to sort by I'm no longer doing an alphabetical sort, which means this problem no longer exists.

  console.log([2,3,4,11].sort((a,b)=>a-b));

Output:
  (4) [2, 3, 4, 11]

The sort() method sorts the elements of an array in place and returns the array. The default sort order is built upon converting the elements into strings, then comparing their sequences of UTF-16 code units values.

developer.mozilla.org/en-US/docs/W...

bugb • Feb 26 '19

yes, by including compareFunction callback, we can solve this problem.

Andy Zhao (he/him) • Feb 21 '19

If it outputs the closest number, it works! :)

Dian Fay • Feb 20 '19

Window functions!

SELECT unnest
FROM unnest(ARRAY[100,200,400,800,1600,3200,6400,128000])
ORDER BY row_number() OVER (ORDER BY abs(900 - unnest))
LIMIT 1;

rhymes • Feb 20 '19

hahaha thinking outside the box :D

Dian Fay • Feb 21 '19

I looked at it again just now and the row_number is redundant anyway...

SELECT unnest
FROM unnest(ARRAY[100,200,400,800,1600,3200,6400,128000])
ORDER BY abs(900 - unnest)
LIMIT 1;

JavaScript Joel • Feb 21 '19 • Edited

This is a job for Reduce!

JavaScript:

const nums = [100, 200, 400, 800, 1600, 3200, 6400, 128000]
const given_num = 900

const closestReducer = g => (a, b) =>
  Math.abs(g - a) < Math.abs(g - b) ? a : b

nums.reduce(closestReducer(given_num))
//=> 800

Andy Zhao (he/him) • Feb 20 '19 • Edited

Ruby:

nums.min_by { |num| (given_num - num).abs }
#=> 800

Shamelessly taken from Stack Overflow 🙃 I was in a much more of a "just give me the answer" mood than "let's figure it out" mood.

Harshit • Feb 20 '19 • Edited

Java:

        int[] nums = {100, 200, 400, 800, 1600, 3200, 6400, 128000};
        int ans = 0;
        int given_num = 900;
        int minDistance = Integer.MAX_VALUE;
        for (int i =0; i < nums.length; i++) {
            int curDistance = Math.abs(nums[i] - given_num);
            if (curDistance < minDistance) {
                ans = nums[i];
                minDistance = curDistance;
            }
        }
        System.out.println(ans);

Trying to optimize no of lines with Java 8 Streams and Lambda.

Aamir Nazir • Feb 25 '19

A Python implementation:

import numpy as np
def find_nearest(array, value):
    array = np.asarray(array)
    idx = (np.abs(array - value)).argmin()
    return array[idx]

nums = [100, 200, 400, 800, 1600, 3200, 6400, 128000]
given_num = 900

print(find_nearest(nums, given_num))

Mikhail Korolev • Feb 21 '19

Wolfram Language!

Nearest[nums, given_num]

I knew that one day my subscription will come in handy...

Gabriel Wu • Feb 22 '19 • Edited

Using JavaScript Set:

const closest_num = (nums, given_num) => {
  const min_dist = Math.min(...nums.map(num => Math.abs(num - given_num)))
  return new Set(nums).has(given_num - min_dist) ? given_num - min_dist : given_num + min_dist
}

Gabriel Wu • Feb 22 '19 • Edited

Or we can save the intermediate array:

const closest_num = (nums, given_num) => {
  const absolute_dists = nums.map(num => Math.abs(num - given_num))
  const min_absolute_dist = Math.min(...absolute_dists)
  return nums[absolute_dists.indexOf(min_absolute_dist)]
}

Pierre Bouillon • Feb 21 '19 • Edited

Here goes Python !

min(nums, key=lambda x: abs(x - given_num))

Gabriel Wu • Feb 22 '19 • Edited

And there is another perspective, instead of iterating numbers, we can iterate distances. Like:

const closest_num = (nums, given_num) => {
  const set = new Set(nums)
  let i = 0
  while (true) {
    if (set.has(given_num - i)) return given_num - i
    if (set.has(given_num + i)) return given_num + i
    i++
  }
}

This will normally be slower, but in cases like:

nums = [10000000, 9999999, 9999998, ..., 1]
given_num = 10000001

It will be much faster than other algorithms.

I have written a benchmark function for this:

const benchmark = (func) => {
  console.time(func.name)
  func.call(this, Array.from({length: 10000000}, (v, idx) => (10000000 - idx)), 10000001)
  console.timeEnd(func.name)
}

You can test your function via benchmark(func).

The solution above yields:

closest_num: 5037.456787109375ms

in Chrome.

Kenneth Lum • Feb 23 '20 • Edited

It looks like the array is sorted. If it is sorted, then the following should be optimal:

Binary search for the left insertion point, and then for the right insertion point.

If found, then that's the answer.

Otherwise, check the left or right number and see which one is closer to the target.

Time complexity: O(log n)

Nikolaus • Oct 16 '19 • Edited

Swift is the most elegant concise and bestest language... ;)

nums.reduce(nums[0]) { abs($0-given_num) < abs($1-given_num) ? $0 : $1 }

Of course in actual usage we would make this an extension and check the validity of the array. I came across this post because I needed it so this one's for CGFloat, which is a Swift floating point type (Double, really)

extension CGFloat {    
    func nearest(arr: [CGFloat]) -> CGFloat {
        guard arr.count > 0 else {
            fatalError("array cannot be empty")
        }
        return arr.reduce(arr[0]) { abs($0-self) < abs($1-self) ? $0 : $1 } 
    }
}

let nums: [CGFloat] = [100, 200, 400, 800, 1600, 3200, 6400, 128000] 
let given_num = CGFloat(900)

let nearest = given_num.nearest(nums)

E. Choroba • Mar 9 '19

Perl solution:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use List::AllUtils qw{ min_by };

my @nums = (100, 200, 400, 800, 1600, 3200, 6400, 128000);
my $given_num = 900;

say $nums[ min_by { abs($nums[$_] - $given_num) } 0 .. $#nums ];

James Hickey • Feb 22 '19

Here's some C# for everyone:

var nums = new int[] { 100, 200, 400, 800, 1600, 3200, 6400, 128000 };
var given_num = 900;

var result = 
    (
        from num in nums
        let diff = Math.Abs(given_num - num)
        orderby diff
        select num
    )
    .First();

bugb • Feb 21 '19 • Edited

nums = [100, 200, 400, 800, 1600, 3200, 6400, 128000];
given_num = 900

Here is my solution:

f = a => (m=Math.min(...nums.map(v=>Math.abs(v-given_num))),nums.find(v=>v==given_num - m || v== m-given_num))

Usage:

f(nums)

Result:

Gabriel Wu • Feb 22 '19 • Edited

Be careful that ... can cause a range error:

RangeError: Maximum call stack size exceeded

when the nums array is very large.

Vicente G. Reyes • Feb 21 '19 • Edited

With the help of google, I was able to find the answer to this 😅

import numpy as np
def find_nearest(array, value):
array = np.array(array)
z=np.abs(array-value)
y= np.where(z == z.min())
m=np.array(y)
x=m[0,0]
y=m[1,0]
near_value=array[x,y]

return near_value

array =np.array([[100, 200, 400, 800, 1600, 3200, 6400, 128000]])
print(array)
value = 900
print(find_nearest(array, value))

Answer:

Thanks for this challenge! 🍺

vorsprung • Feb 22 '19

package main


import (
        "fmt"
        "sort"
)

func main() {
        l := []int{100, 200, 400, 800, 901, 1600, 3200, 6400, 128000}
        target := 900
        n := sort.SearchInts(l, target)
        if l[n]-target < target-l[n-1] {
                n += 1
        }
        fmt.Printf("%d\n", l[n-1])
}

play.golang.org/p/xxzN4y-fPF0

Ayoub Fakir • Feb 22 '19 • Edited

Hey! Let's do it the Scala way:

def closestNumber(x: Int, y: Int, givenNumber: Int): Int = {
    if(abs(givenNumber-x) > abs(givenNumber-y)) {
        y
    } else {
        x
    }
}

val givenNumber = 900
val nums = List(100, 200, 400, 800, 1600, 3200, 6400, 128000)
println(nums.reduce((x, y) => closestNumber(x, y, givenNumber)))
//==> Prints 800

Thanks for the challenge!

Modaf • Feb 21 '19

OCaml with list instead of array

let rec closest num list = match list with
[] -> failwith "Empty list"
|[n] -> n
|h :: q ->
    let closest_q = closest num q in
    let val_h = abs (num - h) in
    let val_q = abs (num - closest_q) in
    if (val_h < val_q) then h else closest_q;;

Dmitry Yakimenko • Feb 21 '19 • Edited

C++, O(n), no sorting, no extra memory allocation beyond storing the input:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> v{100, 200, 400, 800, 1600, 3200, 6400, 128000};
    int given_num = 900;

    cout << *min_element(
        v.begin(), 
        v.end(), 
        [=](int a, int b){ return abs(a - given_num) < abs(b - given_num); }
    );

    return 0;
}

Gabriel Wu • Feb 22 '19

What if there are two numbers that are equally close to the given number?
I think you should point this out in the description.

kip • Feb 21 '19

Rust 🦀

numbers.iter().min_by_key(|&num| (num - given_num).abs()).unwrap()

Andy Zhao (he/him) • Feb 21 '19

Nice, didn't know Rust had similar syntax to Ruby!

Maegan Wilson • Feb 20 '19

I probably over complicated it, but here's a CodePen link with how I did it in JS and outputted it to the HTML side.

Andy Zhao (he/him) • Feb 21 '19

Long as you solved it! 👍

Andrey Vladikin • Feb 20 '19

JS:

const nums = [100, 200, 400, 800, 1600, 3200, 6400, 128000];
const givenNum = 900;

nums
.map(n => ({n, d: Math.abs(n-givenNum)}))
.sort((n1, n2) => Math.sign(n1.d - n2.d))[0].n

Gabriel Wu • Feb 22 '19

If the given array is ascending/descending, then the task becomes a binary search.

The pleasure of programming lies in that even those things appearing to be very simple are also worth thinking.

vorsprung • Feb 23 '19

yeah, that's why I used a binary search library function in my answer :)