diff --git a/Week_01/id_9/LeetCode_104_9.java b/Week_01/id_9/LeetCode_104_9.java
new file mode 100644
index 00000000..3b4b762e
--- /dev/null
+++ b/Week_01/id_9/LeetCode_104_9.java
@@ -0,0 +1,39 @@
+package com.github.lifelab.leetcode.problemset;
+
+/**
+ * 二叉树的最大深度 @https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-03
+ */
+public class Solution104 {
+
+    public int maxDepth(TreeNode root) {
+        return depth(root, 0);
+    }
+
+    private int depth(TreeNode node, int depth) {
+
+        if (node == null) {
+            return 0;
+        }
+
+        depth++;
+
+        if (node.left == null && node.right == null) {
+            return depth;
+        }
+
+        int l = 0, r = 0;
+
+        if (node.left != null) {
+            l = depth(node.left, depth);
+        }
+
+        if (node.right != null) {
+            r = depth(node.right, depth);
+        }
+
+        return Math.max(l, r);
+    }
+}
diff --git a/Week_01/id_9/LeetCode_236_9.java b/Week_01/id_9/LeetCode_236_9.java
new file mode 100644
index 00000000..19b5f34a
--- /dev/null
+++ b/Week_01/id_9/LeetCode_236_9.java
@@ -0,0 +1,39 @@
+package com.github.lifelab.leetcode.problemset;
+
+/**
+ * 二叉树的最近公共祖先 @https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-09
+ */
+public class Solution236 {
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+
+        if (root == null) {
+            return null;
+        }
+
+        if (root.val == p.val || root.val == q.val) {
+            return root;
+        }
+
+        TreeNode leftVal = lowestCommonAncestor(root.left, p, q);
+
+        TreeNode rightVal = lowestCommonAncestor(root.right, p, q);
+
+        if (rightVal != null && leftVal != null) {
+            return root;
+        }
+
+        if (rightVal != null) {
+            return rightVal;
+        }
+
+        if (leftVal != null) {
+            return leftVal;
+        }
+        return null;
+    }
+
+}
diff --git a/Week_01/id_9/LeetCode_26_9.java b/Week_01/id_9/LeetCode_26_9.java
new file mode 100644
index 00000000..0dd92c4c
--- /dev/null
+++ b/Week_01/id_9/LeetCode_26_9.java
@@ -0,0 +1,33 @@
+package com.github.lifelab.leetcode.problemset;
+
+/**
+ * 删除排序数组中的重复项 @https://leetcode-cn.com/problems/remove-duplicates-from-sorted-array/
+ *
+ * @author weichao.li (liweichao0102@gmail.com)
+ * @since 2019-06-04
+ */
+public class Solution26 {
+
+    /**
+     * 1 1 1 2 3 4 4 4
+     *
+     * @param nums
+     * @return
+     * @
+     */
+    public int removeDuplicates(int[] nums) {
+        if (nums == null || nums.length == 0) {
+            return 0;
+        }
+        int left = 0;
+        for (int i = 1; i < nums.length; i++) {
+            if (nums[left] != nums[i]) {
+                left++;
+                nums[left] = nums[i];
+            }
+        }
+        return left + 1;
+    }
+
+
+}
\ No newline at end of file
diff --git a/Week_01/id_9/LeetCode_50_9.java b/Week_01/id_9/LeetCode_50_9.java
new file mode 100644
index 00000000..850ff8d9
--- /dev/null
+++ b/Week_01/id_9/LeetCode_50_9.java
@@ -0,0 +1,46 @@
+package com.github.lifelab.leetcode.problemset;
+
+/**
+ * Pow(x, n) @https://leetcode-cn.com/problems/powx-n/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-06
+ */
+public class Solution50 {
+
+    public double myPow(double x, int n) {
+
+        if (n < 0) {
+            return 1 / halfPow(x, -n);
+        } else {
+            return halfPow(x, n);
+        }
+
+    }
+
+    public double halfPow(double x, int n) {
+
+        //terminator
+        if (n == 0) {
+            return 1;
+        }
+        if (n == 1) {
+            return x;
+        }
+        //process && drill down
+
+        double result;
+
+        boolean flag = n % 2 == 0;
+
+        double temp = halfPow(x, n / 2);
+
+        if (flag) {
+            result = temp * temp;
+        } else {
+            result = temp * temp * x;
+        }
+
+        return result;
+    }
+}
\ No newline at end of file
diff --git a/Week_01/id_9/NOTE.md b/Week_01/id_9/NOTE.md
index 107ea7d6..01582ef8 100644
--- a/Week_01/id_9/NOTE.md
+++ b/Week_01/id_9/NOTE.md
@@ -1 +1,3 @@
 # 学习笔记
+
+> 在 LeetCode 刷题的过程中，可对部分题进行变形简化处理逻辑。
\ No newline at end of file
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