add solution of 204

204. Count Primes
- https://leetcode.com/problems/count-primes/
- https://leetcode.com/explore/challenge/card/may-leetcoding-challenge-2021/599/week-2-may-8th-may-14th/3738/

Author: rushirg

count-primes.py

@@ -0,0 +1,21 @@
+"""
+204. Count Primes
+- https://leetcode.com/problems/count-primes/
+- https://leetcode.com/explore/challenge/card/may-leetcoding-challenge-2021/599/week-2-may-8th-may-14th/3738/
+"""
+
+# Method 1
+# Using Sieve of Eratosthenes algorithm
+
+class Solution:
+    def countPrimes(self, n: int) -> int:
+        if n < 2:
+            return 0
+        isPrime = [1] * n
+        isPrime[0] = isPrime[1] = 0
+        for i in range(2, n):
+            if isPrime[i]:
+                for j in range(i * i, n, i):
+                    isPrime[j] = 0
+        return sum(isPrime)
+