diff --git a/hackerrank/smart-interviews/a-power-b/input.txt b/hackerrank/smart-interviews/a-power-b/input.txt
new file mode 100644
index 0000000..924bb7d
--- /dev/null
+++ b/hackerrank/smart-interviews/a-power-b/input.txt
@@ -0,0 +1,5 @@
+4
+5 2
+1 10
+2 30
+10 10
\ No newline at end of file
diff --git a/hackerrank/smart-interviews/a-power-b/main.cpp b/hackerrank/smart-interviews/a-power-b/main.cpp
new file mode 100644
index 0000000..1f2a233
--- /dev/null
+++ b/hackerrank/smart-interviews/a-power-b/main.cpp
@@ -0,0 +1,30 @@
+#include <fstream>
+
+using namespace std;
+
+constexpr const unsigned long mod = 1000000007;
+
+unsigned long power(unsigned short a, unsigned short b) {
+    if(b == 0)
+        return 1ul;
+    if(b == 1)
+        return static_cast<unsigned long>(a);
+    unsigned long hpower = power(a, b >> 1);
+    return (hpower * ((hpower * (b % 2 == 1 ? a : 1)) % mod)) % mod;
+}
+
+int main() {
+
+    unsigned int T;
+    unsigned short a, b;
+    fstream fin("../input.txt"), fout("../output.txt", ios::out);
+
+    fin >> T;
+
+    while(T--)
+        fin >> a >> b, fout << power(a, b) << endl;
+
+    fin.close(), fout.close();
+
+    return 0;
+}
\ No newline at end of file
diff --git a/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/input.txt b/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/input.txt
new file mode 100644
index 0000000..6c8bb93
--- /dev/null
+++ b/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/input.txt
@@ -0,0 +1,7 @@
+3
+5
+1 2 3 4 5
+5
+3 2 4 1 5
+7
+4 5 15 2 1 7 17
\ No newline at end of file
diff --git a/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/main.cpp b/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/main.cpp
new file mode 100644
index 0000000..3c2470c
--- /dev/null
+++ b/hackerrank/smart-interviews/sum-of-numbers-from-root-to-leaf-paths/main.cpp
@@ -0,0 +1,115 @@
+#include <fstream>
+#include <vector>
+
+using namespace std;
+
+using elem_type = unsigned int;
+
+constexpr const unsigned long mod = 1000000007;
+
+template<typename T, typename R = unsigned long>
+class BST {
+
+    using elem_type = T;
+    using return_type = R;
+
+public:
+
+    BST(): root(nullptr) {}
+
+    explicit BST(const vector<elem_type> & v): root(nullptr) {
+        for(const elem_type & elem : v)
+            this->add(elem);
+    }
+
+    inline ~BST() {
+        delete this->root;
+    }
+
+    void add(elem_type elem) {
+        if(this->root)
+            this->root->add(elem);
+        else
+            this->root = new BSTNode(elem);
+    }
+
+    inline return_type get_sums() const {
+        if(!this->root)
+            return { static_cast<return_type>(0) };
+        return this->root->get_sums();
+    }
+
+private:
+
+    struct BSTNode {
+
+        elem_type elem;
+        BSTNode *right, *left;
+
+        explicit BSTNode(elem_type t_elem):
+                elem(move(t_elem)),
+                right(nullptr),
+                left(nullptr)
+        {}
+
+        inline ~BSTNode() {
+            delete this->left, delete this->right;
+        }
+
+        void add(elem_type elem) {
+            if(elem < this->elem) {
+                if(!this->left)
+                    this->left = new BSTNode(elem);
+                else
+                    this->left->add(elem);
+            }
+            else {
+                if(!this->right)
+                    this->right = new BSTNode(elem);
+                else
+                    this->right->add(elem);
+            }
+        }
+
+        return_type get_sums(return_type curr_value = static_cast<return_type>(0)) const {
+
+            elem_type elem = this->elem;
+
+            while(elem)
+                curr_value = (curr_value * 10) % mod, elem /= 10;
+
+            return_type new_value = (curr_value + this->elem) % mod;
+
+            if(!this->left and !this->right)
+                return new_value;
+
+            return_type left_result = this->left ? this->left->get_sums(new_value) : static_cast<return_type>(0);
+            return_type right_result = this->right ? this->right->get_sums(new_value) : static_cast<return_type>(0);
+            return (left_result + right_result) % mod;
+        }
+
+    };
+
+    BSTNode * root;
+};
+
+int main() {
+
+    unsigned int T, N;
+    fstream fin("../input.txt"), fout("../output.txt", ios::out);
+
+    fin >> T;
+
+    while(T--) {
+        fin >> N;
+        elem_type tmp;
+        vector<elem_type> v;
+        while(N--)
+            fin >> tmp, v.push_back(tmp);
+        fout << BST<elem_type>{v}.get_sums() << endl;
+    }
+
+    fin.close(), fout.close();
+
+    return 0;
+}
\ No newline at end of file