# Using operations to produce desired results in JavaScript

## Problem

We are required to write a JavaScript function that takes in an array of exactly 4 numbers, arr, as the first argument and a target as the second argument.

Our function need to judge whether the numbers in the array arr could operated through *, /, +, -, (, ) to get the value equal to target.

For example, if the input to the function is

Input

const arr = [5, 3, 2, 1];
const target = 4;

Output

const output = true;

Output Explanation

Because we can achieve 4 like this −

(5 - 1) * (3 - 2) = 4

## Example

Following is the code −

Live Demo

const arr = [5, 3, 2, 1];
const target = 4;
const canOperate = (arr = [], target = 1) => {
const isValid = x => Math.abs(x - target) < 0.0000001
const helper = (arr = []) => {
if (arr.length === 1) {
return isValid(arr[0])
}
let valid = false
for (let i = 0; i < arr.length; i++) {
for (let j = i + 1; j < arr.length; j++) {
const nextArr = arr.filter((x, index) => index !== i && index !== j)
valid = valid || helper([...nextArr, arr[i] + arr[j]])
|| helper([...nextArr, arr[i] - arr[j]])
|| helper([...nextArr, arr[j] - arr[i]])
|| helper([...nextArr, arr[i] * arr[j]])
|| helper([...nextArr, arr[i] / arr[j]])
|| helper([...nextArr, arr[j] / arr[i]])
}
}
return valid
}
return helper(arr)
}
console.log(canOperate(arr, target));

## Output

true