add js solution for 204

Author: limbowandering

solution/204.Count Primes/Solution.js

@@ -0,0 +1,31 @@
+// 600ms多
+const countPrimes2 = function(n){
+  let arr = [];
+  let res = 0;
+  for(let i = 2; i < n; i++){
+    if(arr[i] === undefined){
+      arr[i] = 1;
+      res++;
+      for(let j = 2; i * j < n; j++){
+        arr[i * j] = 0;
+      }
+    }
+  }
+  return res;
+};
+
+//200ms多
+const countPrimes = function(n){
+  let arr = [];
+  let res = 0;
+  for(let i = 2; i < n; i++){
+    if(arr[i] === undefined){
+      arr[i] = 1;
+      res++;
+      for(let j = i; i * j < n; j++){
+        arr[i * j] = 0;
+      }
+    }
+  }
+  return res;
+};