Create 010.js

Author: Walker30263

010.js

@@ -0,0 +1,51 @@
+/*
+Source: https://projecteuler.net/problem=10
+
+Problem:
+"The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
+
+Find the sum of all the primes below two million."
+
+
+My Algorithm:
+1. Use the Sieve of Eratosthenes method to generate prime numbers
+The algorithm in a gif: https://upload.wikimedia.org/wikipedia/commons/b/b9/Sieve_of_Eratosthenes_animation.gif
+2. Execute a reducer function to add up all the numbers in the array of prime numbers
+*/
+
+function sieveOfEratosthenes(n) {
+    let numbersUntilN = []
+    let upperLimit = Math.sqrt(n);
+    let primesUntilN = [];
+
+    for (let i = 0; i < n; i++) {
+        numbersUntilN.push(true); //makes an array from 2 to n-1
+    }
+
+    for (let i = 2; i <= upperLimit; i++) {
+        if (numbersUntilN[i]) {
+            for (let j = i * i; j < n; j += i) {
+                numbersUntilN[j] = false; //"cross out" the numbers that are multiples of i, like in the algorithm gif https://upload.wikimedia.org/wikipedia/commons/b/b9/Sieve_of_Eratosthenes_animation.gif
+            }
+        }
+    }
+    
+    
+    //after the "crossing-out" is done, push the ones that are left to the primesUntilN array
+    for (let i = 2; i < n; i++) {
+        if(numbersUntilN[i]) {
+            primesUntilN.push(i);
+        }
+    }
+
+    return primesUntilN;
+}
+
+function solution(n) {
+  let primesUntilN = sieveOfEratosthenes(n);
+
+  const add = (a, b) => a + b;
+  return primesUntilN.reduce(add);
+}
+
+console.log(solution(2000000)); //outputs the answer!