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算法题（国外版）/lowest-common-ancestor-of-a-binary-tree.html

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+<p>Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.</p>
+
+<p>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 <b>a node to be a descendant of itself</b>).&rdquo;</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2018/12/14/binarytree.png" style="width: 200px; height: 190px;" />
+<pre>
+<strong>Input:</strong> root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The LCA of nodes 5 and 1 is 3.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2018/12/14/binarytree.png" style="width: 200px; height: 190px;" />
+<pre>
+<strong>Input:</strong> root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
+<strong>Output:</strong> 5
+<strong>Explanation:</strong> The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> root = [1,2], p = 1, q = 2
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li>The number of nodes in the tree is in the range <code>[2, 10<sup>5</sup>]</code>.</li>
+	<li><code>-10<sup>9</sup> &lt;= Node.val &lt;= 10<sup>9</sup></code></li>
+	<li>All <code>Node.val</code> are <strong>unique</strong>.</li>
+	<li><code>p != q</code></li>
+	<li><code>p</code> and <code>q</code> will exist in the tree.</li>
+</ul>