Merge pull request #936 from zhicheng-lee/master

Update 0236.二叉树的最近公共祖先.md

problems/0236.二叉树的最近公共祖先.md

@@ -221,42 +221,30 @@ public:
 
 
 ## Java 
+
 ```Java
 class Solution {
     public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
-        return lowestCommonAncestor1(root, p, q);
+        if (root == null || root == p || root == q) { // 递归结束条件
-    }
-    public TreeNode lowestCommonAncestor1(TreeNode root, TreeNode p, TreeNode q) {
-        if (root == null || root == p || root == q) {
             return root;
         }
-        TreeNode left = lowestCommonAncestor1(root.left, p, q);
+
-        TreeNode right = lowestCommonAncestor1(root.right, p, q);
+        // 后序遍历
-        if (left != null && right != null) {// 左右子树分别找到了，说明此时的root就是要求的结果
+        TreeNode left = lowestCommonAncestor(root.left, p, q);
-            return root;
+        TreeNode right = lowestCommonAncestor(root.right, p, q);
-        }
+
-        if (left == null) {
+        if(left == null && right == null) { // 若未找到节点 p 或 q
+            return null;
+        }else if(left == null && right != null) { // 若找到一个节点
             return right;
+        }else if(left != null && right == null) { // 若找到一个节点
+            return left;
+        }else { // 若找到两个节点
+            return root;
         }
-        return left;
     }
 }
-```
 
-
-```java
-// 代码精简版
-class Solution {
-    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
-        if (root == null || root.val == p.val ||root.val == q.val) return root;
-        TreeNode left = lowestCommonAncestor(root.left,p,q);
-        TreeNode right = lowestCommonAncestor(root.right,p,q);
-        if (left != null && right != null) return root;
-        else if (left == null && right != null) return right;
-        else if (left != null && right == null) return left;
-        else return null;
-    }
-}
 ```
 
 ## Python 

problems/0701.二叉搜索树中的插入操作.md

@@ -236,16 +236,13 @@ class Solution {
 ```java
 class Solution {
     public TreeNode insertIntoBST(TreeNode root, int val) {
-        return buildTree(root, val);
-    }
-
-    public TreeNode buildTree(TreeNode root, int val){
         if (root == null) // 如果当前节点为空，也就意味着val找到了合适的位置，此时创建节点直接返回。
             return new TreeNode(val);
+            
         if (root.val < val){
-            root.right = buildTree(root.right, val); // 递归创建右子树
+            root.right = insertIntoBST(root.right, val); // 递归创建右子树
         }else if (root.val > val){
-            root.left = buildTree(root.left, val); // 递归创建左子树
+            root.left = insertIntoBST(root.left, val); // 递归创建左子树
         }
         return root;
     }