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;
}