solves count primes

Author: anishLearnsToCode

Diff for: README.md

@@ -62,7 +62,7 @@
 | 198 | [House Robber](https://leetcode.com/problems/house-robber) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/HouseRobber.java) |
 | 202 | [Happy Number](https://leetcode.com/problems/happy-number) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/HappyNumber.java) | 
 | 203 | [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/RemoveLinkedListElements.java) |
-| 204 | [Count Primes](https://leetcode.com/problems/count-primes) | Easy |
+| 204 | [Count Primes](https://leetcode.com/problems/count-primes) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)]() |
 | 205 | [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings) | Easy |
 | 206 | [Reverse Linked Lists](https://leetcode.com/problems/reverse-linked-list) | Easy |
 | 217 | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate) | Easy |

Diff for: src/CountPrimes.java

@@ -0,0 +1,33 @@
+public class CountPrimes {
+
+    public static int countPrimes(int number) {
+        boolean[] sieve = getSieve(number);
+        return numberOfPrimes(sieve);
+    }
+
+    private static int numberOfPrimes(boolean[] array) {
+        int count = 0;
+        for (boolean value : array) {
+            if (!value) count++;
+        }
+        return count;
+    }
+
+    private static boolean[] getSieve(int number) {
+        if (number < 2) {
+            return new boolean[0];
+        }
+
+        boolean[] sieve = new boolean[number];
+        sieve[0] = sieve[1] = true;
+        for (long index = 2 ; index < sieve.length ; index++){
+            if (!sieve[(int) index]) {
+                for (long j = index * index ; j < sieve.length ; j += index) {
+                    sieve[(int) j] = true;
+                }
+            }
+        }
+
+        return sieve;
+    }
+}