add cpp version(use set)

Author: zouwx2cs

solution/0961.N-Repeated Element in Size 2N Array/Solution2.cpp

@@ -0,0 +1,10 @@
+class Solution {
+public:
+    int repeatedNTimes(vector<int>& A) {
+        for(int i  = (A.size() >> 1) - 1; i < A.size(); ++i)
+            for(int j = i+1; j < A.size(); ++j)
+                if(A[i] == A[j])
+                    return A[i];
+        return A[0] ;
+    }
+};