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Andy Zhao (he/him)

Posted on

# Challenge: Get Closest Number in an Array

Given an array of numbers `nums`, and a given number `given_num`:

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

Get the number closest to the `given_num` from the array `nums`.

In this example, the returned value should be `800`.

# Go!

## Discussion (36)

Andrew Bone • Edited on

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 • Edited on

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

``````[2,3,4,11].sort()
``````
Andrew Bone

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

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

Andy Zhao (he/him)

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

Dian Fay

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

hahaha thinking outside the box :D

Dian Fay

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;
``````
Andy Zhao (he/him) • Edited on

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.

JavaScript Joel • Edited on

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
``````
Harshit • Edited on

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.

Mikhail Korolev

Wolfram Language!

``````Nearest[nums, given_num]
``````

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

Aamir Nazir

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))
``````
Pierre Bouillon • Edited on

Here goes Python !

``````min(nums, key=lambda x: abs(x - given_num))
``````
Gabriel Wu • Edited on

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 • Edited on

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)]
}
``````
Gabriel Wu • Edited on

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.

E. Choroba

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 ];
``````
vorsprung
``````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 • Edited on

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!

Vicente Reyes • Edited on

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))

Thanks for this challenge! 🍺

Modaf

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 • Edited on

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;
}
``````

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)

``````
bugb • Edited on

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:

``````800
``````
Gabriel Wu • Edited on

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

`RangeError: Maximum call stack size exceeded`

when the `nums` array is very large.

Kenneth Lum • Edited on

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)

James Hickey

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();
``````
Gabriel Wu

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

Rust 🦀

``````numbers.iter().min_by_key(|&num| (num - given_num).abs()).unwrap()
``````
Andy Zhao (he/him)

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

Maegan Wilson

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)

Long as you solved it! 👍

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

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

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