package Question4_7;
import CtCILibrary.TreeNode;
public class Question {
static int TWO_NODES_FOUND = 2;
static int ONE_NODE_FOUND = 1;
static int NO_NODES_FOUND = 0;
// Checks how many �special� nodes are located under this root
public static int covers(TreeNode root, TreeNode p, TreeNode q) {
int ret = NO_NODES_FOUND;
if (root == null) return ret;
if (root == p || root == q) ret += 1;
ret += covers(root.left, p, q);
if(ret == TWO_NODES_FOUND) // Found p and q
return ret;
return ret + covers(root.right, p, q);
}
public static TreeNode commonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if (q == p && (root.left == q || root.right == q)) return root;
int nodesFromLeft = covers(root.left, p, q); // Check left side
if (nodesFromLeft == TWO_NODES_FOUND) {
if(root.left == p || root.left == q) return root.left;
else return commonAncestor(root.left, p, q);
} else if (nodesFromLeft == ONE_NODE_FOUND) {
if (root == p) return p;
else if (root == q) return q;
}
int nodesFromRight = covers(root.right, p, q); // Check right side
if(nodesFromRight == TWO_NODES_FOUND) {
if(root.right == p || root.right == q) return root.right;
else return commonAncestor(root.right, p, q);
} else if (nodesFromRight == ONE_NODE_FOUND) {
if (root == p) return p;
else if (root == q) return q;
}
if (nodesFromLeft == ONE_NODE_FOUND &&
nodesFromRight == ONE_NODE_FOUND) return root;
else return null;
}
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(1);
TreeNode n7 = root.find(7);
TreeNode ancestor = commonAncestor(root, n3, n7);
System.out.println(ancestor.data);
}
}