public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
{
pst = new Stack<TreeNode>();
qst = new Stack<TreeNode>();
if (root == null) return null;
TreeNode result, ptr = root;
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, pst);
qb = isChildOf(ptr, q, qst);
result = root;
while(true){
if (pst.Count == 0 || qst.Count == 0 || pst.Peek() != qst.Peek()) return result;
else
{
result = pst.Pop();
qst.Pop();
}
}
}
static void Main(string[] args)
{
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;
n3.right = n7;
Program p = new Program();
Console.WriteLine(p.LowestCommonAncestor(root, n3, n7).val);
Console.ReadKey();
}
private bool isChildOf(TreeNode ance, TreeNode child, Stack<TreeNode> stack)
{
//bool result = false;
if (ance == child)
{
//result = true;
stack.Push(ance);
return true;
}
if (ance.left != null && isChildOf(ance.left, child, stack))
{
//result = true;
stack.Push(ance);
return true;
}
if (ance.right != null && isChildOf(ance.right, child, stack))
{
//result = true;
stack.Push(ance);
return true;
}
return false;
}