binary-tree-inorder-traversal——二叉树中序遍历

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

For example:
Given binary tree{1,#,2,3},

   1
    
     2
    /
   3

return[1,3,2].

/**
 * Definition for binary tree
 * 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> res;
        if(root==NULL) return res;
        stack<TreeNode*> s;
        TreeNode* cur=root;
        while(cur||!s.empty()){
            while(cur!=NULL){
                s.push(cur);
                cur=cur->left;
            }
            cur=s.top();
            s.pop();
            res.push_back(cur->val);
            cur=cur->right;
        }
        return res;
    }
    
};