204

Author: LeuisKen

204.js

@@ -0,0 +1,26 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var countPrimes = function(n) {
+	if(n <= 2) return 0;
+	n = n - 2;
+	var prime = [], res = 1;
+	for(var i = 0; i < n>>1; i++){
+		prime.push(true);
+	}
+	var k = n>>1, m = parseInt(Math.sqrt(n));
+	for(i = 0; i <= m; i++){
+		if(prime[i]){
+			for(var j = 2*i*i+6*i+3; j<=k; j+=2*i+3){
+				prime[j] = false;
+			}
+		}
+	}
+	for(i = 0; i < n>>1; i++){
+		if(prime[i] === true){
+			res++;
+		}
+	}
+	return res;
+};