/*
This is an implementation that collects the
values of the nodes of a binary tree by performing
an in-order traversal of the tree.
Let n be the number of binary tree nodes
Time complexity: O(n)
Space complexity: O(n)
*/
import java.util.List;
import java.util.ArrayList;
public class BTInOrderTraversal {
private BTNode BTRoot;
public BTInOrderTraversal() {
/*
* Create tree below:
* 1
*
* 2
* /
* 3
*/
BTRoot = new BTNode(1, null, null);
BTNode rootRight = new BTNode(2, null, null);
BTRoot.right = rootRight;
BTNode rootRightLeft = new BTNode(3, null, null);
rootRight.left = rootRightLeft;
}
public static void main(String[] args) {
BTInOrderTraversal application = new BTInOrderTraversal();
List<Integer> values = application.inorderTraversal();
System.out.println(values); // [1, 3, 2]
}
// Perform in-order traversal through the tree.
public List<Integer> inorderTraversal() {
List<Integer> list = new ArrayList<>();
populateList(BTRoot, list);
return list;
}
// Helper method to populate list by performing
// in-order traversal through the tree.
private void populateList(BTNode root, List<Integer> list) {
if (root == null) {
return;
}
if (root.left != null) {
populateList(root.left, list);
}
list.add(root.val);
if (root.right != null) {
populateList(root.right, list);
}
}
// Class representing a binary tree node
// with pointers to value, left, and right nodes
private class BTNode {
int val;
BTNode left;
BTNode right;
public BTNode(int val, BTNode left, BTNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}