Add construct balanced binary tree

Author: rp-code9

README.md

@@ -111,6 +111,7 @@ Princeton Algorithms [Part 1](https://www.coursera.org/learn/algorithms-part1/)
 ## Binary Tree
 * Binary tree
     * Recursive Preorder, inorder, postorder, height, diameter [C++](problems/binary-tree/BasicTree.cpp)
+* Construct balanced binary tree [C++](problems/binary-tree/ConstructBalancedTree.cpp)
 * Find longest increasing path in binary tree [C++](problems/binary-tree/LongestPathInBinaryTree.cpp)
 * Find longest increasing path in n-ary tree [C++](problems/binary-tree/LongestPathInNaryTree.cpp)
 

problems/binary-tree/ConstructBalancedTree.cpp

@@ -0,0 +1,76 @@
+// Techie Delight https://www.techiedelight.com/construct-balanced-bst-given-keys/
+
+#include <vector>
+#include <iostream>
+
+class Tree
+{
+private:
+    class Node
+    {
+    public:
+        int key;
+        Node* left;
+        Node* right;
+
+        Node(int k) : key(k), left(nullptr), right(nullptr) { }
+    };
+
+    Node* root;
+
+    void print(std::vector<Node*>& path)
+    {
+        for (auto node : path) {
+            std::cout << node->key << " ";
+        }
+        std::cout << "\n";
+    }
+
+    void preorder(Node* node, std::vector<Node*>& path)
+    {
+        if (node == nullptr) {
+            return;
+        }
+        path.push_back(node);
+        preorder(node->left, path);
+        preorder(node->right, path);
+    }
+
+    Node* construct(std::vector<int>& keys, int left, int right)
+    {
+        if (left > right) {
+            return nullptr;
+        }
+
+        int mid = left + (right - left) / 2;
+        Node* node = new Node(keys[mid]);
+
+        node->left = construct(keys, left, mid - 1);
+        node->right = construct(keys, mid + 1, right);
+
+        return node;
+    }
+
+public:
+    Tree() : root(nullptr) { }
+
+    Tree(std::vector<int> keys)
+    {
+        root = construct(keys, 0, keys.size() - 1);
+    }
+
+    void inorder()
+    {
+        std::vector<Node*> path;
+        preorder(root, path);
+        print(path);
+    }
+
+};
+
+int main()
+{
+    std::vector<int> keys { 15, 10, 20, 8, 12, 16, 25 };
+    Tree tree(keys);
+    tree.inorder();
+}