binary-tree-preorder-traversal: add C++ solution (azl397985856#27)

Author: raof01

problems/125.valid-palindrome.md

@@ -48,6 +48,10 @@ Output: false
 
 ## 代码
 
+* 语言支持：JS，C++
+
+JavaScript Code:
+
 ```js
 
 /*
@@ -94,3 +98,22 @@ var isPalindrome = function(s) {
   return right <= left;
 };
 ```
+C++ Code:
+```C++
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        if (s.empty())
+            return true;
+        const char* s1 = s.c_str();
+        const char* e = s1 + s.length() - 1;
+        while (e > s1) {
+            if (!isalnum(*s1)) {++s1; continue;}
+            if (!isalnum(*e)) {--e; continue;}
+            if (tolower(*s1) != tolower(*e)) return false;
+            else {--e; ++s1;}
+        }
+        return true;
+    }
+};
+```

problems/144.binary-tree-preorder-traversal.md

@@ -48,6 +48,10 @@ mid是一个具体的节点，left和right`递归求出即可`
 
 ## 代码
 
+* 语言支持：JS，C++
+
+JavaScript Code:
+
 ```js
 /*
  * @lc app=leetcode id=144 lang=javascript
@@ -121,4 +125,32 @@ var preorderTraversal = function(root) {
 };
 
 ```
-
+C++ Code:
+```C++
+/**
+ * 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<int> preorderTraversal(TreeNode* root) {
+        vector<int> v;
+        vector<TreeNode*> s;
+        while (root != NULL || !s.empty()) {
+            while (root != NULL) {
+                v.push_back(root->val);
+                s.push_back(root);
+                root = root->left;
+            }
+            root = s.back()->right;
+            s.pop_back();
+        }
+        return v;
+    }
+};
+```