QuestionA.java

package Q4_08_First_Common_Ancestor;

import CtCILibrary.TreeNode;

public class QuestionA {
	public static TreeNode commonAncestor(TreeNode p, TreeNode q) {
		if (p == q) return p;
		
		TreeNode ancestor = p;
		while (ancestor != null) {
			if (isOnPath(ancestor, q)) {
				return ancestor;
			}
			ancestor = ancestor.parent;
		}
		return null;
	}
	
	public static boolean isOnPath(TreeNode ancestor, TreeNode node) {
		while (node != ancestor && node != null) {
			node = node.parent;
		}
		return node == ancestor;
	}	
	
	public static void main(String[] args) {
		int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
		TreeNode root = TreeNode.createMinimalBST(array);
		TreeNode n3 = root.find(8);
		TreeNode n7 = root.find(8);
		TreeNode ancestor = commonAncestor(n3, n7);
		System.out.println(ancestor.data);
	}

}