94. Binary Tree Inorder Traversa

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