diff --git a/0043_multiply_strings/multiply_strings.cc b/0043_multiply_strings/multiply_strings.cc
index 77436e4..0ca6c59 100644
--- a/0043_multiply_strings/multiply_strings.cc
+++ b/0043_multiply_strings/multiply_strings.cc
@@ -5,23 +5,29 @@ using namespace std;
 class Solution {
 public:
     string multiply(string num1, string num2) {
-        string res(num1.length() + num2.length(), '0');
+        vector<int> v(num1.length() + num2.length());
         for (int i = num2.length() - 1; i >= 0; i--) {
-            int j, carry = 0;
-            for (j = num1.length() - 1; j >= 0; j--) {
-                carry += (num1[j] - '0') * (num2[i] - '0') + (res[i + j + 1] - '0');
-                res[i + j + 1] = carry % 10 + '0';
-                carry /= 10;
+            for (int j = num1.length() - 1; j >= 0; j--) {
+                int a = num2[j] - '0';
+                int b = num1[i] - '0';
+                v[i + j + 1] = a * b;
             }
-            res[i + j + 1] = carry + '0';
         }
 
-        int i;
+        int i, carry = 0;
+        string res(v.size(), '0');
+        for (i = v.size() - 1; i >= 0; i--) {
+            carry += v[i];
+            res[i] += carry % 10;
+            carry /= 10;
+        }
+
         for (i = 0; i < res.length() - 1; i++) {
             if (res[i] != '0') {
                 break;
             }
         }
+
         return res.substr(i);
     }
 };
diff --git a/0131_palindrome_patitioning/palindrome_partition.cc b/0131_palindrome_patitioning/palindrome_partition.cc
new file mode 100644
index 0000000..9897ddb
--- /dev/null
+++ b/0131_palindrome_patitioning/palindrome_partition.cc
@@ -0,0 +1,42 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<string>> partition(string s) {
+        vector<vector<string>> res;
+        vector<vector<bool>> isPalindrome(s.size(), vector<bool>(s.size(), true));
+
+        // From bottom to up
+        for (int i = s.length() - 1; i >= 0; i--) {
+            // From left to right
+            for (int j = i + 1; j < s.length(); j++) {
+                // notebook for palindrome substring judgement
+                isPalindrome[i][j] = s[i] == s[j] && isPalindrome[i + 1][j - 1];
+            }
+        }
+
+        dfs(s, 0, isPalindrome, res);
+        return res;
+    }
+
+private:
+    vector<string> ans;
+    void dfs(const string& s, int start, vector<vector<bool>>& isPalindrome, vector<vector<string>>& res) {
+        // DFS for combination. When the start index reaches to the end, all
+        // the substrings are collected.
+        if (start == s.length()) {
+            res.push_back(ans);
+            return;
+        }
+
+        for (int i = start; i < s.length(); i++) {
+            if (isPalindrome[start][i]) {
+                ans.push_back(s.substr(start, i - start + 1));
+                dfs(s, i + 1, isPalindrome, res);
+                ans.pop_back();
+            }
+        }
+    }
+};
diff --git a/0133_clone_graph/clone_graph.cc b/0133_clone_graph/clone_graph.cc
new file mode 100644
index 0000000..ca7d8e2
--- /dev/null
+++ b/0133_clone_graph/clone_graph.cc
@@ -0,0 +1,65 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+// Definition for a Node.
+class Node {
+public:
+    int val;
+    vector<Node*> neighbors;
+    Node() {
+        val = 0;
+        neighbors = vector<Node*>();
+    }
+    Node(int _val) {
+        val = _val;
+        neighbors = vector<Node*>();
+    }
+    Node(int _val, vector<Node*> _neighbors) {
+        val = _val;
+        neighbors = _neighbors;
+    }
+};
+
+class Solution {
+public:
+    Node* cloneGraph(Node* node) {
+        if (node == nullptr) {
+            return node;
+        }
+#if 1 // DFS
+        if (cloned.find(node) != cloned.end()) {
+            return cloned[node];
+        }
+
+        cloned[node] = new Node(node->val);
+
+        for (auto& neighbor : node->neighbors) {
+            cloned[node]->neighbors.emplace_back(cloneGraph(neighbor));
+        }
+#else // BFS
+        queue<Node *> q;
+        q.push(node);
+        cloned[node] = new Node(node->val);
+
+        while (!q.empty()) {
+            int size = q.size();
+            for (int i = 0; i < size; i++) {
+                auto n = q.front();
+                q.pop();
+
+                for (auto& neighbor : n->neighbors) {
+                    if (cloned.find(neighbor) == cloned.end()) {
+                        cloned[neighbor] = new Node(neighbor->val);
+                        q.push(neighbor);
+                    }
+                    cloned[n]->neighbors.emplace_back(cloned[neighbor]);
+                }
+            }
+        }
+#endif
+        return cloned[node];
+    }
+private:
+    unordered_map<Node *, Node *> cloned;   
+};
diff --git a/0567_permutation_in_string/permutation_in_string.cc b/0567_permutation_in_string/permutation_in_string.cc
index 541b1cb..1061ae6 100644
--- a/0567_permutation_in_string/permutation_in_string.cc
+++ b/0567_permutation_in_string/permutation_in_string.cc
@@ -10,18 +10,20 @@ class Solution {
             count[c]++;
         }
 
-        int l = 0, r = 0, len = 0;
+        int l = 0, r = 0, hits = 0;
         while (r < s2.length()) {
             if (--count[s2[r++]] >= 0) {
-                len++;
+                hits++;
             }
 
+            // When the window length equals to the hit length,
+            // the permutation is contained.
             if (r - l >= s1.length()) {
-                if (len == s1.length()) {
+                if (hits == s1.length()) {
                     return true;
                 }
                 if (++count[s2[l++]] > 0) {
-                    len--;
+                    hits--;
                 }
             }
         }