Create a balanced binary search tree from a sorted array (Fixes: TheAlgorithms#2706) (TheAlgorithms#2711)

Co-authored-by: Amit Kumar <[email protected]>

Author: kumanoit

DataStructures/Trees/CreateBSTFromSortedArray.java

@@ -0,0 +1,45 @@
+package DataStructures.Trees;
+
+import DataStructures.Trees.BinaryTree.Node;
+
+/**
+ * Given a sorted array. Create a balanced binary search tree from it.
+ *
+ * Steps:
+ * 1. Find the middle element of array. This will act as root
+ * 2. Use the left half recursively to create left subtree
+ * 3. Use the right half recursively to create right subtree
+ */
+public class CreateBSTFromSortedArray {
+
+  public static void main(String[] args) {
+    test(new int[]{});
+    test(new int[]{1, 2, 3});
+    test(new int[]{1, 2, 3, 4, 5});
+    test(new int[]{1, 2, 3, 4, 5, 6, 7});
+  }
+
+  private static void test(int[] array) {
+    BinaryTree root = new BinaryTree(createBst(array, 0, array.length - 1));
+    System.out.println("\n\nPreorder Traversal: ");
+    root.preOrder(root.getRoot());
+    System.out.println("\nInorder Traversal: ");
+    root.inOrder(root.getRoot());
+    System.out.println("\nPostOrder Traversal: ");
+    root.postOrder(root.getRoot());
+  }
+
+  private static Node createBst(int[] array, int start, int end) {
+    // No element left.
+    if (start > end) {
+      return null;
+    }
+    int mid = start + (end - start) / 2;
+
+    // middle element will be the root
+    Node root = new Node(array[mid]);
+    root.left = createBst(array, start, mid - 1);
+    root.right = createBst(array, mid + 1, end);
+    return root;
+  }
+}