diff --git a/Week_01/id_41/LeetCode_101_41.cpp b/Week_01/id_41/LeetCode_101_41.cpp
new file mode 100644
index 00000000..b923043c
--- /dev/null
+++ b/Week_01/id_41/LeetCode_101_41.cpp
@@ -0,0 +1,30 @@
+/*
+ * @lc app=leetcode id=101 lang=cpp
+ *
+ * [101] Symmetric Tree
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    bool isSymmetric(TreeNode* root) {
+        return root == NULL || isSymmetricHelp(root->left, root->right);
+    }
+    bool isSymmetricHelp(TreeNode* left, TreeNode* right) {
+        if (left == NULL || right == NULL) {
+            return left == right;
+        }
+        if (left->val != right->val) {
+            return false;
+        }
+        return isSymmetricHelp(left->left, right->right) && isSymmetricHelp(left->right, right->left);
+    }
+};
+
diff --git a/Week_01/id_41/LeetCode_104_41.cpp b/Week_01/id_41/LeetCode_104_41.cpp
new file mode 100644
index 00000000..8061d492
--- /dev/null
+++ b/Week_01/id_41/LeetCode_104_41.cpp
@@ -0,0 +1,22 @@
+/*
+ * @lc app=leetcode id=104 lang=cpp
+ *
+ * [104] Maximum Depth of Binary Tree
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution
+{
+public:
+    int maxDepth(TreeNode *root)
+    {
+        return (root == nullptr) ? 0 : max(maxDepth(root->left), maxDepth(root->right)) + 1;
+    }
+};
diff --git a/Week_01/id_41/LeetCode_111_41.cpp b/Week_01/id_41/LeetCode_111_41.cpp
new file mode 100644
index 00000000..f2460186
--- /dev/null
+++ b/Week_01/id_41/LeetCode_111_41.cpp
@@ -0,0 +1,26 @@
+/*
+ * @lc app=leetcode id=111 lang=cpp
+ *
+ * [111] Minimum Depth of Binary Tree
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution
+{
+public:
+    int minDepth(TreeNode *root)
+    {
+        if (root == NULL)
+            return 0;
+        int left = minDepth(root->left);
+        int right = minDepth(root->right);
+        return (left == 0 || right == 0) ? (left + right + 1) : min(left, right) + 1;
+    }
+};
diff --git a/Week_01/id_41/LeetCode_174_41.cpp b/Week_01/id_41/LeetCode_174_41.cpp
new file mode 100644
index 00000000..e154f14c
--- /dev/null
+++ b/Week_01/id_41/LeetCode_174_41.cpp
@@ -0,0 +1,26 @@
+/*
+ * @lc app=leetcode id=174 lang=cpp
+ *
+ * [174] Dungeon Game
+ */
+class Solution {
+public:
+    int calculateMinimumHP(vector<vector<int> > &dungeon) {
+        int M = dungeon.size();
+        int N = dungeon[0].size();
+        // hp[i][j] represents the min hp needed at position (i, j)
+        // Add dummy row and column at bottom and right side
+        vector<vector<int> > hp(M + 1, vector<int>(N + 1, INT_MAX));
+        hp[M][N - 1] = 1;
+        hp[M - 1][N] = 1;
+        for (int i = M - 1; i >= 0; i--) {
+            for (int j = N - 1; j >= 0; j--) {
+                int need = max(1, min(hp[i + 1][j], hp[i][j + 1])) - dungeon[i][j];
+                hp[i][j] = need <= 0 ? 1 : need;
+            }
+        }
+        return hp[0][0];
+    }
+};
+
+
diff --git a/Week_01/id_41/LeetCode_257_41.cpp b/Week_01/id_41/LeetCode_257_41.cpp
new file mode 100644
index 00000000..27566968
--- /dev/null
+++ b/Week_01/id_41/LeetCode_257_41.cpp
@@ -0,0 +1,38 @@
+/*
+ * @lc app=leetcode id=257 lang=cpp
+ *
+ * [257] Binary Tree Paths
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<string> binaryTreePaths(TreeNode* root) {
+        vector<string> answer;
+        if (root != nullptr) {
+            searchBT(root, "", answer);
+        }
+        return answer;
+    }
+
+private:
+    void searchBT(TreeNode* root, string path, vector<string>& answer) {
+        if (root->left == nullptr && root->right == nullptr) {
+            answer.push_back(path + to_string(root->val));            
+        }
+        if (root->left != nullptr) {
+            searchBT(root->left, path + to_string(root->val) + "->", answer);
+        }
+        if (root->right != nullptr) {
+            searchBT(root->right, path + to_string(root->val) + "->", answer);
+        }
+    }
+};
+
diff --git a/Week_01/id_41/LeetCode_263_41.cpp b/Week_01/id_41/LeetCode_263_41.cpp
new file mode 100644
index 00000000..828f6b13
--- /dev/null
+++ b/Week_01/id_41/LeetCode_263_41.cpp
@@ -0,0 +1,20 @@
+/*
+ * @lc app=leetcode id=263 lang=cpp
+ *
+ * [263] Ugly Number
+ */
+class Solution
+{
+public:
+    bool isUgly(int num)
+    {
+        for (int i = 2; i < 6 && (num != 0); i++)
+        {
+            while (num % i == 0)
+            {
+                num /= i;
+            }
+        }
+        return num == 1;
+    }
+};
diff --git a/Week_01/id_41/LeetCode_26_41.cpp b/Week_01/id_41/LeetCode_26_41.cpp
new file mode 100644
index 00000000..77f08c6d
--- /dev/null
+++ b/Week_01/id_41/LeetCode_26_41.cpp
@@ -0,0 +1,21 @@
+/*
+ * @lc app=leetcode id=26 lang=cpp
+ *
+ * [26] Remove Duplicates from Sorted Array
+ */
+class Solution {
+public:
+    int removeDuplicates(vector<int>& nums) {
+        int i = 0;
+        for (int j = 0; j < nums.size(); j++)
+        {
+            if (!i || nums[j] > nums[i-1])
+            {
+                nums[i] = nums[j];
+                i++;
+            }
+        }
+        return i;
+    }
+};
+
diff --git a/Week_01/id_41/LeetCode_338_41.cpp b/Week_01/id_41/LeetCode_338_41.cpp
new file mode 100644
index 00000000..b0184b50
--- /dev/null
+++ b/Week_01/id_41/LeetCode_338_41.cpp
@@ -0,0 +1,17 @@
+/*
+ * @lc app=leetcode id=338 lang=cpp
+ *
+ * [338] Counting Bits
+ */
+class Solution {
+public:
+    vector<int> countBits(int num) {
+        vector<int> bits(num + 1, 0);
+        for (int i = 1; i <= num; ++i)
+        {
+            bits[i] += bits[i & (i - 1)] + 1;
+        }
+        return bits;
+    }
+};
+
diff --git a/Week_01/id_41/LeetCode_441_41.cpp b/Week_01/id_41/LeetCode_441_41.cpp
new file mode 100644
index 00000000..7e62ad9e
--- /dev/null
+++ b/Week_01/id_41/LeetCode_441_41.cpp
@@ -0,0 +1,17 @@
+/*
+ * @lc app=leetcode id=441 lang=cpp
+ *
+ * [441] Arranging Coins
+ */
+class Solution {
+public:
+    int arrangeCoins(int n) {
+        int i = 1;
+        while (n >= i) {
+            n -= i;
+            i++;
+        }
+        return i - 1;
+    }
+};
+
diff --git a/Week_01/id_41/LeetCode_50_41.cpp b/Week_01/id_41/LeetCode_50_41.cpp
new file mode 100644
index 00000000..bec58ced
--- /dev/null
+++ b/Week_01/id_41/LeetCode_50_41.cpp
@@ -0,0 +1,20 @@
+/*
+ * @lc app=leetcode id=50 lang=cpp
+ *
+ * [50] Pow(x, n)
+ */
+class Solution
+{
+public:
+    double myPow(double x, int n)
+    {
+        if (n == 0)
+            return 1;
+        if (n < 0)
+        {
+            n = -n;
+            x = 1 / x;
+        }
+        return (n & 1) ? pow(x * x, n / 2) * x : pow(x * x, n / 2);
+    }
+};
diff --git a/Week_01/id_41/LeetCode_783_41.cpp b/Week_01/id_41/LeetCode_783_41.cpp
new file mode 100644
index 00000000..243fd761
--- /dev/null
+++ b/Week_01/id_41/LeetCode_783_41.cpp
@@ -0,0 +1,31 @@
+/*
+ * @lc app=leetcode id=783 lang=cpp
+ *
+ * [783] Minimum Distance Between BST Nodes
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution
+{
+public:
+    int res = INT_MAX;
+    int preVal = -1;
+    int minDiffInBST(TreeNode *root)
+    {
+        if (root->left != NULL)
+            minDiffInBST(root->left);
+        if (preVal >= 0)
+            res = min(res, root->val - preVal);
+        preVal = root->val;
+        if (root->right != NULL)
+            minDiffInBST(root->right);
+        return res;
+    }
+};
diff --git a/Week_01/id_41/LeetCode_938_41.cpp b/Week_01/id_41/LeetCode_938_41.cpp
new file mode 100644
index 00000000..ff24b300
--- /dev/null
+++ b/Week_01/id_41/LeetCode_938_41.cpp
@@ -0,0 +1,28 @@
+/*
+ * @lc app=leetcode id=938 lang=cpp
+ *
+ * [938] Range Sum of BST
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution
+{
+public:
+    int rangeSumBST(TreeNode *root, int L, int R)
+    {
+        if (root == nullptr)
+            return 0;
+        if (root->val > R)
+            return rangeSumBST(root->left, L, R);
+        if (root->val < L)
+            return rangeSumBST(root->right, L, R);
+        return root->val + rangeSumBST(root->left, L, R) + rangeSumBST(root->right, L, R);
+    }
+};
diff --git a/Week_01/id_41/NOTE.md b/Week_01/id_41/NOTE.md
index 107ea7d6..f159ed65 100644
--- a/Week_01/id_41/NOTE.md
+++ b/Week_01/id_41/NOTE.md
@@ -1 +1,3 @@
 # 学习笔记
+递归代码看着的确很清爽。
+C写起来会很累，CPP的vector<vector<int>>二维数组比C动态分配数组来通过指针计算方便很多。
diff --git a/algo.png b/algo.png
new file mode 100644
index 00000000..8079f7a5
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