Add C++ solution of problem #2657

Author: Cuda-Chen

2657/solution.cpp

@@ -0,0 +1,15 @@
+class Solution {
+public:
+    vector<int> findThePrefixCommonArray(vector<int>& A, vector<int>& B) {
+        int n = A.size();
+        vector<int> ans(n);
+        uint64_t a = 0, b = 0; // hash map
+        for(int i = 0; i < n; i++) {
+            a |= (1LL << A[i]);
+            b |= (1LL << B[i]);
+            uint64_t c = a & b;
+            ans[i] = __builtin_popcountll(c);
+        }
+        return ans;
+    }
+};