Question

Write an algorithm to find the ‘next’ node (i.e., in-order successor) of a given node in a binary search tree where each node has a link to its parent.

Solution

  1. If current node have a right child, return the leftmost leaf of right child.

  2. If current node have no right child:

    1. If current is parent’s left child, then return parent node.

    2. If current is parent’s right child, look all the way up until find a right-turning parent.

    3. If all parent is not right-turning. Return null.

Code

written by me

public static TreeNode inorderSucc(TreeNode e) {
	if (e == null)
		return null;
	if (e.right != null) {
		TreeNode p = e.right;
		while (p.left != null) {
			p = p.left;
		}
		return p;
	} else {
		TreeNode p = e.parent;
		while (p != null && p.right == e) {
			e = p;
			p = e.parent;
		}
		return p;
	}
}