LeetCode：94_Binary Tree Inorder Traversal | 二叉树中序遍历 | Medium

题目：Binary Tree Inorder Traversal

二叉树的中序遍历，和前序、中序一样的处理方式，代码见下：

 struct TreeNode {
     int            val;
     TreeNode*    left;
     TreeNode*    right;
     TreeNode(int x): val(x), left(NULL),right(NULL) {}
 };

 vector<int> preorderTraversal(TreeNode *root) //非递归的中序遍历(用栈实现)
 {
     if (NULL == root) {
         return vector<int>();
     }

     stack<TreeNode *> tree_stack;
     vector<int> tree_vector;

     TreeNode *pTemp = root;
     while (pTemp || !tree_stack.empty()) {
         while (pTemp) {
             tree_stack.push(pTemp);
             pTemp = pTemp->left;
         }
         if (!tree_stack.empty()) {
             pTemp = tree_stack.top();
             tree_vector.push_back(pTemp->val);
             tree_stack.pop();
             pTemp = pTemp->right;
         }
     }
     return tree_vector;
 }