java: add «236. Lowest Common Ancestor of a Binary Tree»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/lowest-common-ancestor-of-a-binary-tree.java

@@ -0,0 +1,24 @@
+class Solution {
+  public TreeNode lowestCommonAncestor(TreeNode node, TreeNode p, TreeNode q) {
+    if (node == null) {
+      return null;
+    }
+
+    if (node.val == p.val || node.val == q.val) {
+      return node;
+    }
+
+    var left = lowestCommonAncestor(node.left, p, q);
+    var right = lowestCommonAncestor(node.right, p, q);
+
+    if (left == null) {
+      return right;
+    }
+
+    if (right == null) {
+      return left;
+    }
+
+    return node;
+  }
+}