add solution

Author: Neil94n

solution/0268.Missing Number/Solution2.js

@@ -0,0 +1,19 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var missingNumber = function(nums) {
+    var flags = []  
+    for(var i = 0; i <= nums.length; i++) {
+        flags[i] = 0
+    }   
+    for(var i = 0; i<nums.length; i++) {
+        var num = nums[i]
+        flags[ num ] = 1
+    }    
+    for(var i = 0; i < flags.length; i++) {
+        if (flags[i] == 0) {
+            return i
+        }
+    }    
+};