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Finding all possible prime pairs that sum upto input number using JavaScript
Problem
We are required to write a JavaScript function that takes in a number n. Our function should return an array of all such number pairs that when summed are n and both of them are prime.
Example
Following is the code −
const num = 26;
const isPrime = (n) => {
if (n % 2 === 0) return false;
let sqrtn = Math.sqrt(n)+1;
for (let i=3; i < sqrtn; i+=2) {
if (n % i === 0) return false;
}
return true;
}
const primeList = (a) => {
if (isPrime(a)) return a; else return false;
};
const generateNumbers = (n) => {
let num = (n % 2 === 0) ? (n -1) : n;
let list = []
for (let i = num; i > 3; i-=2)
list.push(i);
list.push(3,1);
return list;
}
const calculate = (num, list, results) => {
if (list.length === 0) return results;
let item = list.shift();
let itemPairIndex = list.indexOf(num - item);
if (itemPairIndex !== -1) {
let itemPair = list.splice(itemPairIndex,1)
results.push(item+"+"+itemPair);
}
return calculate(num, list, results);
}
const findprimeSum = (num) => {
const pairs = [];
const list = generateNumbers(num).filter(primeList);
return calculate(num, list, []);
}
console.log(findprimeSum(num));Output
[ '23+3', '19+7' ]
Updated on: 19-Apr-2021
464 Views
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