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45 changes: 45 additions & 0 deletions DataStructures/Trees/CreateBSTFromSortedArray.java
Original file line number Diff line number Diff line change
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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;
}
}