diff --git a/5.leetcode/src/com/fanxb/common/Q144.java b/5.leetcode/src/com/fanxb/common/Q144.java
new file mode 100644
index 0000000..6dba935
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q144.java
@@ -0,0 +1,21 @@
+package com.fanxb.common;
+
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
+
+public class Q144 {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> res = new LinkedList<>();
+        if (root == null) return res;
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        while (!stack.isEmpty()) {
+            TreeNode node = stack.pop();
+            res.add(node.val);
+            if (node.right != null) stack.push(node.right);
+            if (node.left != null) stack.push(node.left);
+        }
+        return res;
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q145.java b/5.leetcode/src/com/fanxb/common/Q145.java
new file mode 100644
index 0000000..ede47ee
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q145.java
@@ -0,0 +1,25 @@
+package com.fanxb.common;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Stack;
+
+public class Q145 {
+    public List<Integer> postorderTraversal(TreeNode root) {
+        List<Integer> res = new ArrayList<>();
+        if (root == null) return res;
+        Stack<Integer> helpStack = new Stack<>();
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        while (!stack.isEmpty()) {
+            TreeNode node = stack.pop();
+            helpStack.push(node.val);
+            if (node.left != null) stack.push(node.left);
+            if (node.right != null) stack.push(node.right);
+        }
+        while (!helpStack.isEmpty()) {
+            res.add(helpStack.pop());
+        }
+        return res;
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q230.java b/5.leetcode/src/com/fanxb/common/Q230.java
new file mode 100644
index 0000000..ab2887b
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q230.java
@@ -0,0 +1,20 @@
+package com.fanxb.common;
+
+public class Q230 {
+    private int res = 0;
+    private int count = 0;
+
+    public int kthSmallest(TreeNode root, int k) {
+        dfs(root, k);
+        return res;
+    }
+
+    private void dfs(TreeNode root, int k) {
+        if (root == null) return;
+        dfs(root.left, k);
+        if (++count == k) {
+            res = root.val;
+        }
+        dfs(root.right, k);
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q380.java b/5.leetcode/src/com/fanxb/common/Q380.java
new file mode 100644
index 0000000..5a890f8
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q380.java
@@ -0,0 +1,45 @@
+package com.fanxb.common;
+
+import java.util.*;
+
+public class Q380 {
+    private static class RandomizedSet {
+        private List<Integer> list;
+        private Map<Integer, Integer> map;
+        private Random random;
+
+        public RandomizedSet() {
+            list = new ArrayList<>();
+            map = new HashMap<>();
+            random = new Random();
+        }
+
+        public boolean insert(int val) {
+            Integer index = map.get(val);
+            if (index != null) return false;
+            list.add(val);
+            map.put(val, list.size() - 1);
+            System.out.println(list.toString());
+            return true;
+        }
+
+        public boolean remove(int val) {
+            Integer index = map.get(val);
+            if (index == null) return false;
+            int last = list.size() - 1;
+            int lastVal = list.get(last);
+            list.set(index, lastVal);
+            list.remove(last);
+            map.remove(val);
+            //避免长度为1时将删除的元素放到map
+            if (!list.isEmpty()) map.put(lastVal, index);
+            System.out.println(list.toString());
+            return true;
+        }
+
+        public int getRandom() {
+            int size = list.size();
+            return size == 1 ? list.get(0) : list.get(Math.abs(random.nextInt()) % size);
+        }
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q530.java b/5.leetcode/src/com/fanxb/common/Q530.java
new file mode 100644
index 0000000..40123a9
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q530.java
@@ -0,0 +1,21 @@
+package com.fanxb.common;
+
+public class Q530 {
+    private int res = Integer.MAX_VALUE;
+    private Integer lastVal = null;
+
+    public int getMinimumDifference(TreeNode root) {
+        dfs(root);
+        return res;
+    }
+
+    private void dfs(TreeNode root) {
+        if (root == null) return;
+        dfs(root.left);
+        if (lastVal != null) {
+            res = Math.min(res, Math.abs(root.val - lastVal));
+        }
+        lastVal = root.val;
+        dfs(root.right);
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q94.java b/5.leetcode/src/com/fanxb/common/Q94.java
new file mode 100644
index 0000000..f54a2a6
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q94.java
@@ -0,0 +1,25 @@
+package com.fanxb.common;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Stack;
+
+public class Q94 {
+    public List<Integer> inorderTraversal(TreeNode root) {
+        List<Integer> res = new ArrayList<>();
+        if (root == null) return res;
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        TreeNode cur = root.left;
+        while (!stack.isEmpty() || cur != null) {
+            while (cur != null) {
+                stack.push(cur);
+                cur = cur.left;
+            }
+            TreeNode node = stack.pop();
+            res.add(node.val);
+            cur = node.right;
+        }
+        return res;
+    }
+}
diff --git a/5.leetcode/src/com/fanxb/common/Q98.java b/5.leetcode/src/com/fanxb/common/Q98.java
new file mode 100644
index 0000000..6bd73f7
--- /dev/null
+++ b/5.leetcode/src/com/fanxb/common/Q98.java
@@ -0,0 +1,20 @@
+package com.fanxb.common;
+
+public class Q98 {
+    private Integer lastVal = null;
+
+    public boolean isValidBST(TreeNode root) {
+        return dfs(root);
+    }
+
+    private boolean dfs(TreeNode root) {
+        if (root == null) return true;
+        boolean left = dfs(root.left);
+        if (lastVal != null && lastVal >= root.val) {
+            return false;
+        }
+        lastVal = root.val;
+        boolean right = dfs(root.right);
+        return left && right;
+    }
+}