Leetcode#94 Binary Tree Inorder Traversal

考察非递归写法。前序遍历可以参考这篇文章，后序遍历可以参考这篇

代码：

 1 vector<int> inorderTraversal(TreeNode *root) {
 2         TreeNode *node = NULL;
 3         stack<TreeNode *> st;
 4         vector<int> path;
 5         
 6         node = root;
 7         while (node) {
 8             while (node) {
 9                 st.push(node);
10                 node = node->left;
11             }
12             node = NULL;
13             while (!st.empty() && !node) {
14                 path.push_back(st.top()->val);
15                 node = st.top()->right;
16                 st.pop();
17             }
18         }
19         
20         return path;
21 }