lowest-common-ancestor-of-a-binary-search-tree

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Algorithms

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

According to the <a href="https://en.wikipedia.org/wiki/Lowest_common_ancestor" target="_blank">definition of LCA on Wikipedia</a>: &ldquo;The lowest common ancestor is defined between two nodes <code>p</code> and <code>q</code> as the lowest node in <code>T</code> that has both <code>p</code> and <code>q</code> as descendants (where we allow a node to be a descendant of itself).&rdquo;

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2018/12/14/binarysearchtree_improved.png" style="width: 200px; height: 190px;" />
<pre>
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
Explanation: The LCA of nodes 2 and 8 is 6.
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2018/12/14/binarysearchtree_improved.png" style="width: 200px; height: 190px;" />
<pre>
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
</pre>

Example 3:

<pre>
Input: root = [2,1], p = 2, q = 1
Output: 2
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[2, 105]</code>.</li>
	<li><code>-109 &lt;= Node.val &lt;= 109</code></li>
	<li>All <code>Node.val</code> are unique.</li>
	<li><code>p != q</code></li>
	<li><code>p</code> and <code>q</code> will exist in the BST.</li>
</ul>