diff --git a/construct-binary-tree-from-preorder-and-inorder-traversal/ys-han00.cpp b/construct-binary-tree-from-preorder-and-inorder-traversal/ys-han00.cpp
new file mode 100644
index 0000000000..0901bad65c
--- /dev/null
+++ b/construct-binary-tree-from-preorder-and-inorder-traversal/ys-han00.cpp
@@ -0,0 +1,40 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    unordered_map<int, int> indices;
+    int pre_idx = 0;
+    
+    TreeNode* dfs(const vector<int>& preorder, int start, int end) {
+        if (start > end)
+            return nullptr;
+
+        int root_val = preorder[pre_idx++];
+        TreeNode* root = new TreeNode(root_val);
+
+        int mid = indices[root_val];
+
+        root->left = dfs(preorder, start, mid - 1);
+        root->right = dfs(preorder, mid + 1, end);
+
+        return root;
+    }
+
+    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
+        for (int i = 0; i < inorder.size(); ++i)
+            indices[inorder[i]] = i;
+        
+        pre_idx = 0;
+
+        return dfs(preorder, 0, inorder.size() - 1);
+    }
+};
diff --git a/longest-palindromic-substring/ys-han00.cpp b/longest-palindromic-substring/ys-han00.cpp
new file mode 100644
index 0000000000..0ac72da2a4
--- /dev/null
+++ b/longest-palindromic-substring/ys-han00.cpp
@@ -0,0 +1,26 @@
+class Solution {
+public:
+    string longestPalindrome(string s) {
+        int max_s = 0, max_e = 0;
+        int n = s.size();
+        vector<vector<bool>> dp(n, vector<bool>(n, false));
+        
+        for(int i = n - 1; i >= 0; i--) {
+            for(int j = i; j < n; j++) {
+                if(i == j)
+                    dp[i][j] = true;
+                else if(i + 1 == j)
+                    dp[i][j] = (s[i] == s[j]);
+                else
+                    dp[i][j] = (s[i] == s[j]) && dp[i + 1][j - 1];
+
+                if(dp[i][j] && max_e - max_s < j - i) {
+                    max_s = i;
+                    max_e = j;
+                }
+            }
+        }
+
+        return s.substr(max_s, max_e - max_s + 1);
+    }
+};
diff --git a/rotate-image/ys-han00.cpp b/rotate-image/ys-han00.cpp
new file mode 100644
index 0000000000..82c1d0d591
--- /dev/null
+++ b/rotate-image/ys-han00.cpp
@@ -0,0 +1,19 @@
+class Solution {
+public:
+    void rotate(vector<vector<int>>& matrix) {
+        int top = 0, bottom = matrix.size() - 1;
+
+        while(top < bottom) {
+            int left = top, right = bottom;
+            for(int i = 0; i < bottom - top; i++) {
+                int topLeft = matrix[top][left + i];
+                matrix[top][left + i] = matrix[bottom - i][left];
+                matrix[bottom - i][left] = matrix[bottom][right - i];
+                matrix[bottom][right - i] = matrix[top + i][right];
+                matrix[top + i][right] = topLeft;
+            }
+            top++;
+            bottom--;
+        }
+    }
+};
diff --git a/subtree-of-another-tree/ys-han00.cpp b/subtree-of-another-tree/ys-han00.cpp
new file mode 100644
index 0000000000..1f4c09fa7f
--- /dev/null
+++ b/subtree-of-another-tree/ys-han00.cpp
@@ -0,0 +1,55 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool isSameTree(TreeNode* p, TreeNode* q) {
+        if (p == nullptr && q == nullptr) return true;
+        if (p == nullptr || q == nullptr) return false;
+        if (p->val != q->val) return false;
+
+        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
+    }
+
+    bool isSubtree(TreeNode* root, TreeNode* subRoot) {
+        if (root == nullptr) return false;
+        if (isSameTree(root, subRoot)) return true;
+        return isSubtree(root->left, subRoot) || isSubtree(root->right, subRoot);
+    }
+    
+    // bool ans = false;
+    // void check(TreeNode* root, TreeNode* subRoot) {
+    //     if(root == nullptr || subRoot == nullptr || root->val != subRoot->val) {
+    //         if(root != nullptr || subRoot != nullptr)
+    //             ans = false;
+    //         return;
+    //     }
+    //     check(root->left, subRoot->left);
+    //     check(root->right, subRoot->right);
+    // }
+
+    // void rec(TreeNode* root, TreeNode* subRoot) {
+    //     if(root == nullptr || ans)
+    //         return;
+    //     if(root->val == subRoot->val) {
+    //         ans = true;
+    //         check(root, subRoot);
+    //         if(ans) return;
+    //     }
+    //     rec(root->left, subRoot);
+    //     rec(root->right, subRoot);
+    // }
+
+    // bool isSubtree(TreeNode* root, TreeNode* subRoot) {
+    //     rec(root, subRoot);
+    //     return ans;
+    // }
+};