add codeforces solutions folder

leetcode/lc693/AlternatingCompare.cpp

@@ -0,0 +1,15 @@
+class Solution{
+    public : 
+        bool hasAlternatingBits(int n){
+            bool cur = n%2;
+            n/=2;
+            while(n){
+                if(n%2 == cur) return false;
+                cur = n%2;
+                n/=2;
+            }
+            return true;
+        }
+};
+
+// n%2 extracts the last bit and n/=2 extracts the rest of the bits, now if last bit of the rest of the bits is equal to the current last bit, then two adjacent bits are same and hence we return false

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