add cpp version(do not use set)

Author: zouwx2cs

solution/0961.N-Repeated Element in Size 2N Array/Solution.cpp

@@ -0,0 +1,12 @@
+class Solution {
+public:
+    int repeatedNTimes(vector<int>& A) {
+        unordered_set<int> us(A[0]) ;
+        for(int i  = (A.size() >> 1) - 1; i < A.size(); ++i)
+            if(us.find(A[i]) != us.end())
+                return A[i] ;
+            else
+                us.insert(A[i]) ;
+        return A[0] ;
+    }
+};