diff --git a/problems/0235.二叉搜索树的最近公共祖先.md b/problems/0235.二叉搜索树的最近公共祖先.md
index 929e6eb2..25bbf7e4 100644
--- a/problems/0235.二叉搜索树的最近公共祖先.md
+++ b/problems/0235.二叉搜索树的最近公共祖先.md
@@ -234,7 +234,15 @@ public:
 ## Java 
 
 递归法：
-
+```java
+class Solution {
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root.val > p.val && root.val > q.val) return lowestCommonAncestor(root.left, p, q);
+        if (root.val < p.val && root.val < q.val) return lowestCommonAncestor(root.right, p, q);
+        return root;
+    }
+}
+```
 
 迭代法：
 ```java
diff --git a/problems/0450.删除二叉搜索树中的节点.md b/problems/0450.删除二叉搜索树中的节点.md
index b8a1ae87..b12d40aa 100644
--- a/problems/0450.删除二叉搜索树中的节点.md
+++ b/problems/0450.删除二叉搜索树中的节点.md
@@ -293,6 +293,32 @@ class Solution {
     }
 }
 ```
+```java
+// 解法2
+class Solution {
+  public TreeNode deleteNode(TreeNode root, int key) {
+    if (root == null) return root;
+    if (root.val == key) {
+      if (root.left == null) {
+        return root.right;
+      } else if (root.right == null) {
+        return root.left;
+      } else {
+        TreeNode cur = root.right;
+        while (cur.left != null) {
+          cur = cur.left;
+        }
+        cur.left = root.left;
+        root = root.right;
+        return root;
+      }
+    }
+    if (root.val > key) root.left = deleteNode(root.left, key);
+    if (root.val < key) root.right = deleteNode(root.right, key);
+    return root;
+  }
+}
+```
 
 ## Python 
 
diff --git a/problems/0501.二叉搜索树中的众数.md b/problems/0501.二叉搜索树中的众数.md
index aeddc600..22d4f4ac 100644
--- a/problems/0501.二叉搜索树中的众数.md
+++ b/problems/0501.二叉搜索树中的众数.md
@@ -429,6 +429,44 @@ class Solution {
     }
 }
 ```
+迭代法
+```java
+class Solution {
+    public int[] findMode(TreeNode root) {
+        TreeNode pre = null;
+        Stack<TreeNode> stack = new Stack<>();
+        List<Integer> result = new ArrayList<>();
+        int maxCount = 0;
+        int count = 0;
+        TreeNode cur = root;
+        while (cur != null || !stack.isEmpty()) {
+            if (cur != null) {
+                stack.push(cur);
+                cur =cur.left;
+            }else {
+                cur = stack.pop();
+                // 计数
+                if (pre == null || cur.val != pre.val) {
+                    count = 1;
+                }else {
+                    count++;
+                }
+                // 更新结果
+                if (count > maxCount) {
+                    maxCount = count;
+                    result.clear();
+                    result.add(cur.val);
+                }else if (count == maxCount) {
+                    result.add(cur.val);
+                }
+                pre = cur;
+                cur = cur.right;
+            }
+        }
+        return result.stream().mapToInt(Integer::intValue).toArray();
+    }
+}
+```
 
 ## Python 
 
diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md
index ae6719ec..b19a0dd2 100644
--- a/problems/0530.二叉搜索树的最小绝对差.md
+++ b/problems/0530.二叉搜索树的最小绝对差.md
@@ -171,7 +171,34 @@ class Solution {
     }
 }
 ```
+迭代法-中序遍历
 
+```java
+class Solution {
+    TreeNode pre;
+    Stack<TreeNode> stack;
+    public int getMinimumDifference(TreeNode root) {
+        if (root == null) return 0;
+        stack = new Stack<>();
+        TreeNode cur = root;
+        int result = Integer.MAX_VALUE;
+        while (cur != null || !stack.isEmpty()) {
+            if (cur != null) {
+                stack.push(cur); // 将访问的节点放进栈
+                cur = cur.left; // 左
+            }else {
+                cur = stack.pop(); 
+                if (pre != null) { // 中
+                    result = Math.min(result, cur.val - pre.val);
+                }
+                pre = cur;
+                cur = cur.right; // 右
+            }
+        }
+        return result;
+    }
+}
+```
 ## Python 
 
 递归