Update Problem001.js (TheAlgorithms#1536)

* Update Problem001.js * Update Problem001.js * Update Problem001.js * Update Problem001.js * Update Problem001.js

Author: imrahulkb

Project-Euler/Problem001.js

@@ -1,20 +1,23 @@
 // https://projecteuler.net/problem=1
-/* Multiples of 3 and 5
-If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+/* Multiples of 3 and 5
+If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6, and 9. The sum of these multiples is 23.
 Find the sum of all the multiples of 3 or 5 below the provided parameter value number.
 */
 
+// This method uses the nSum function to add the nSum for 3 and 5. However, it needs to subtract the nSum for 15 once to avoid double counting.
 constmultiplesThreeAndFive=(num)=>{
 if(num<1)thrownewError('No natural numbers exist below 1')
+num-=1
+letsum=0
 
-lettotal=0
-// total for calculating the sum
-for(leti=1;i<num;i++){
-if(i%3===0||i%5===0){
-total+=i
-}
-}
-returntotal
+// The nSum function calculates the sum of the first n numbers in the sequence with a common difference of num.
+// Here, n is denoted as frequency.
+constnSum=(num,frequency)=>(frequency*(frequency+1)*num)>>1
+
+sum+=nSum(3,Math.floor(num/3))
+sum+=nSum(5,Math.floor(num/5))
+sum-=nSum(15,Math.floor(num/15))
+returnsum
 }
 
 export{multiplesThreeAndFive}