static void Main(string[] args)
{
//// 0 1 2
//TreeNode root = new TreeNode(0);
//TreeNode left = new TreeNode(1);
//TreeNode right = new TreeNode(2);
//[5,3,6,1,4,null,null,null,2]
//node with value 4
//node with value 2
TreeNode root = new TreeNode(5);
TreeNode n1 = new TreeNode(3);
TreeNode n2 = new TreeNode(6);
root.left = n1;
root.right = n2;
TreeNode n3 = new TreeNode(1);
TreeNode n4 = new TreeNode(4);
TreeNode n7 = new TreeNode(2);
n1.left = n3;
n1.right = n4;
n4.right = n7;
//root.left = left;
//left.right = right;
Program p = new Program();
Console.WriteLine(p.LowestCommonAncestor(root, n4, n7).val);
Console.ReadKey();
}
private TreeNode findCommonAncestor(TreeNode node, TreeNode p, TreeNode q)
{
if (node == null) return null;
if ((p.val <= node.val && node.val <= q.val)
||
(q.val <= node.val && node.val <= p.val)) return node;
else if (p.val < node.val && q.val < node.val)
{
return findCommonAncestor(node.left, p, q);
}
else if (p.val > node.val && q.val > node.val)
{
return findCommonAncestor(node.right, p, q);
}
else return null;
}
private TreeNode findCommonAncestorByTraverse(TreeNode node, TreeNode p, TreeNode q)
{
if(node == null)return null;
TreeNode result, ptr = node;
bool pb, qb;
// common ance is that both p and q are child
// lowest is that one node that both are true, but not for each of its child
pb = isChildOf(ptr, p);
qb = isChildOf(ptr, q);
if (pb && qb)
{
result = findCommonAncestor(ptr.left, p, q);
if (result != null) return result;
result = findCommonAncestor(ptr.right, p, q);
if (result != null) return result;
return ptr;
}
else return null;
}
//204 ms
public TreeNode LowestCommonAncestorByTraverse(TreeNode root, TreeNode p, TreeNode q)
{
TreeNode result = findCommonAncestor(root, p, q);
if (result == null) return root;
return result;
}
private bool isChildOf(TreeNode ance, TreeNode child)
{
if (ance == child || ance.left == child || ance.right == child) return true;
if (ance.left != null && isChildOf(ance.left, child)) return true;
if (ance.right != null && isChildOf(ance.right, child)) return true;
return false;
}