feat: add cpp solutions to lcof problems: No. 30,31,32

Author: maolonglong

lcof/面试题30. 包含min函数的栈/README.md

@@ -73,21 +73,21 @@ class MinStack {
         mins = new ArrayDeque<>();
         mins.push(Integer.MAX_VALUE);
     }
-    
+
     public void push(int val) {
         s.push(val);
         mins.push(Math.min(mins.peek(), val));
     }
-    
+
     public void pop() {
         s.pop();
         mins.pop();
     }
-    
+
     public int top() {
         return s.peek();
     }
-    
+
     public int min() {
         return mins.peek();
     }
@@ -158,6 +158,42 @@ MinStack.prototype.min = function () {
  */
 ```
 
+### **C++**
+
+```cpp
+class MinStack {
+private:
+    stack<int> a, b;
+
+public:
+    /** initialize your data structure here. */
+    MinStack() {
+    }
+
+    void push(int x) {
+        a.push(x);
+        if (b.empty() || x <= b.top()) {
+            b.push(x);
+        }
+    }
+
+    void pop() {
+        if (a.top() == b.top()) {
+            b.pop();
+        }
+        a.pop();
+    }
+
+    int top() {
+        return a.top();
+    }
+
+    int min() {
+        return b.top();
+    }
+};
+```
+
 ### **...**
 
 ```

lcof/面试题30. 包含min函数的栈/Solution.cpp

@@ -0,0 +1,31 @@
+class MinStack {
+private:
+    stack<int> a, b;
+
+public:
+    /** initialize your data structure here. */
+    MinStack() {
+    }
+
+    void push(int x) {
+        a.push(x);
+        if (b.empty() || x <= b.top()) {
+            b.push(x);
+        }
+    }
+
+    void pop() {
+        if (a.top() == b.top()) {
+            b.pop();
+        }
+        a.pop();
+    }
+
+    int top() {
+        return a.top();
+    }
+
+    int min() {
+        return b.top();
+    }
+};

lcof/面试题31. 栈的压入、弹出序列/README.md

@@ -98,6 +98,26 @@ var validateStackSequences = function (pushed, popped) {
 };
 ```
 
+### **C++**
+
+```cpp
+class Solution {
+public:
+    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
+        stack<int> s;
+        int i = 0;
+        for (int x : pushed) {
+            s.push(x);
+            while (!s.empty() && s.top() == popped[i]) {
+                s.pop();
+                ++i;
+            }
+        }
+        return s.empty();
+    }
+};
+```
+
 ### **...**
 
 ```

lcof/面试题31. 栈的压入、弹出序列/Solution.cpp

@@ -0,0 +1,15 @@
+class Solution {
+public:
+    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
+        stack<int> s;
+        int i = 0;
+        for (int x : pushed) {
+            s.push(x);
+            while (!s.empty() && s.top() == popped[i]) {
+                s.pop();
+                ++i;
+            }
+        }
+        return s.empty();
+    }
+};

lcof/面试题32 - II. 从上到下打印二叉树 II/README.md

@@ -165,6 +165,33 @@ func levelOrder(root *TreeNode) [][]int {
 }
 ```
 
+### **C++**
+
+```cpp
+class Solution {
+public:
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        vector<vector<int>> ans;
+        if (root == NULL) return ans;
+        queue<TreeNode*> q;
+        q.push(root);
+        while (!q.empty()) {
+            int n = q.size();
+            vector<int> v;
+            for (int i = 0; i < n; ++i) {
+                TreeNode* node = q.front();
+                q.pop();
+                v.emplace_back(node->val);
+                if (node->left) q.push(node->left);
+                if (node->right) q.push(node->right);
+            }
+            ans.emplace_back(v);
+        }
+        return ans;
+    }
+};
+```
+
 ### **...**
 
 ```

lcof/面试题32 - II. 从上到下打印二叉树 II/Solution.cpp

@@ -0,0 +1,22 @@
+class Solution {
+public:
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        vector<vector<int>> ans;
+        if (root == NULL) return ans;
+        queue<TreeNode*> q;
+        q.push(root);
+        while (!q.empty()) {
+            int n = q.size();
+            vector<int> v;
+            for (int i = 0; i < n; ++i) {
+                TreeNode* node = q.front();
+                q.pop();
+                v.emplace_back(node->val);
+                if (node->left) q.push(node->left);
+                if (node->right) q.push(node->right);
+            }
+            ans.emplace_back(v);
+        }
+        return ans;
+    }
+};