/*
* January 6, 2016
* blog:
https://github.com/mengli/leetcode/blob/master/LowestCommonAncestorOfaBinarySearchTree.java
*
* Make two changes:
* 1. use short name - LCA
* 2. use Math.Max and Math.Min function
*
*/
public static TreeNode LCA(TreeNode root, TreeNode p, TreeNode q)
{
if (root == null || p == null || q == null) // bug001 fix
return null;
if (root.val < Math.Min(p.val, q.val))
return LCA(root.right, p, q);
else if (root.val > Math.Max(p.val, q.val))
return LCA(root.left, p, q);
else
return root;
}
/*
* Leetcode question 235
* Lowest common ancestor in binary search tree
* January 6, 2016
*
* p or q may be null pointer, so p.val or q.val cannot be accessed.
* Base Case is wrong - Sorry!
*
*/
public static TreeNode lowestCommonAncestor_bug(TreeNode root, TreeNode p, TreeNode q)
{
if (root == null)
return null;
if (root.val < p.val && root.val < q.val)
return lowestCommonAncestor_bug(root.right, p, q);
else if (root.val > p.val && root.val > q.val)
return lowestCommonAncestor_bug(root.left, p, q);
else
return root;
}
static void Main(string[] args)
{
TreeNode n1 = new TreeNode(4);
n1.left = new TreeNode(2);
n1.right = new TreeNode(6);
n1.left.left = new TreeNode(1);
n1.left.right = new TreeNode(3);
n1.right.left = new TreeNode(5);
n1.right.right = new TreeNode(7);
TreeNode r = LCA(n1, n1.right.left, n1.left.right);
TreeNode r2 = LCA(n1, n1.left.left, n1.left.right);
}
public TreeNode(int x)
{
left = null;
right = null;
val = x;
}