problems(cpp): add “1680. Concatenation of Consecutive Binary Numbers”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cpp/concatenation-of-consecutive-binary-numbers.cpp

@@ -0,0 +1,34 @@
+#include <cassert>
+
+class Solution {
+    static const int MOD = 1000000007;
+
+public:
+    int concatenatedBinary(int n)
+    {
+        long joined_number = 0;
+
+        int padding = 1;
+        for (int i = 1; i <= n; i++) {
+            joined_number = ((joined_number << padding) + i) % MOD;
+
+            if ((i & (i + 1)) == 0) {
+                padding++;
+            }
+        }
+
+        return joined_number;
+    }
+};
+
+int main()
+{
+    Solution s;
+
+    assert(s.concatenatedBinary(1) == 1);
+    assert(s.concatenatedBinary(2) == 6);
+    assert(s.concatenatedBinary(3) == 27);
+    assert(s.concatenatedBinary(12) == 505379714);
+
+    return 0;
+}