From 9e688056efbcb434a463bf07a3e43db64ccddbb0 Mon Sep 17 00:00:00 2001
From: Aditya <adi004.zz@gmail.com>
Date: Sun, 11 Nov 2018 20:20:08 +0530
Subject: [PATCH] fix(curriculum): Problem 10 added optimized code (#31066)

---
 .../problem-10-summation-of-primes.english.md | 43 ++++++-------------
 1 file changed, 12 insertions(+), 31 deletions(-)

diff --git a/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-10-summation-of-primes.english.md b/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-10-summation-of-primes.english.md
index 8317feedc99..3b0bc83eb9c 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-10-summation-of-primes.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-10-summation-of-primes.english.md
@@ -49,49 +49,30 @@ primeSummation(2000000);
 
 </div>
 
-
-
 </section>
 
 ## Solution
 <section id='solution'>
 
-
 ```js
 //noprotect
 function primeSummation(n) {
-  // Initialise an array containing only prime numbers
-  let primes = [2];
-  let result = 2;
-
-  function isPrime(y, primes) {
-    // Find sqrt(y)
-    const sqrt = Math.floor(Math.sqrt(y));
-
-    // Divide y by each applicable prime, return false if any of them divide y
-    for (let i = 0; i < primes.length && primes[i] <= sqrt; i++) {
-      if (y % primes[i] === 0) {
-        return false;
-      }
-    }
-
-    // At this point x must be prime
-    return true;
+  if (n < 3) { return 0 };
+  let nums = [0, 0, 2];
+  for (let i = 3; i < n; i += 2){
+    nums.push(i);
+    nums.push(0);
   }
-
-  // For every odd integer, add it to the array if it is prime
-  for (let x = 3; x < n; x += 2) {
-    if (isPrime(x, primes)) {
-      if (x > n) {
-        return result;
-      } else {
-        result += x;
-        primes.push(x);
+  let sum = 2;
+  for (let i = 3; i < n; i += 2){
+    if (nums[i] !== 0){
+      sum += nums[i];
+      for (let j = i*i; j < n; j += i){
+        nums[j] = 0;
       }
     }
   }
-
-  return result;
+  return sum;
 }
 ```