[Leetcode]Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

和preorder是一样的，把左子节点一直压入到栈中，直到没有左子节点为止，然后出栈访问，存储右子节点。

vector<int> inorderTraversal(TreeNode *root) 
{
    vector<int> val;
    stack<TreeNode *> path;
    TreeNode *p = root;    
    while (!path.empty() || p != NULL)
    {
        while (p != NULL)
        {
            path.push(p);
            p = p->left;
        }
        
        if (!path.empty())
        {
            p = path.top();
            path.pop();
            
            val.push_back(p->val);
            
            p = p->right;
        }
    } ;
    
    return val;
}