Update 递归.md

8 Algorithms Analysis/递归.md

@@ -233,6 +233,24 @@ public static LinkedNode mergeSeqLink(LinkedNode l1, LinkedNode l2){
 
 ```Java
 
+TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+    // base case
+    if (root == null) return null;
+    if (root == p || root == q) return root;
+
+    TreeNode left = lowestCommonAncestor(root.left, p, q);
+    TreeNode right = lowestCommonAncestor(root.right, p, q);
+    // 情况 1
+    if (left != null && right != null) {
+        return root;
+    }
+    // 情况 2
+    if (left == null && right == null) {
+        return null;
+    }
+    // 情况 3
+    return left == null ? right : left;
+}
 ```