add codeforces solutions folder

leetcode/lc693/AlternatingXOR.cpp

@@ -0,0 +1,10 @@
+class Solution{
+    public : 
+        bool hasAlternatingBits(int n){
+            int m = n^(n>>1);
+            return (m&(m+1)==0);
+        }
+}
+
+// TC & SC : o(1)
+// n>>1 inverts all bits and XOR makes m have all set bits if n had alternating bits. (m+1) makes all bits of m as zero and m&(m+1) will be zero