【中级算法】10.中序遍历二叉树

给定一个二叉树，返回它的中序 遍历。

示例:

输入: [1,null,2,3]
   1
         2
    /
   3

输出: [1,3,2]
进阶: 递归算法很简单，你可以通过迭代算法完成吗？

/**
 * 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) {
        stack<TreeNode *> myStack;
        vector<int> res;
        
        if(root == NULL){
            return res;
        }
        
        myStack.push(root);
        s = root;
        while(!myStack.empty()&&s){
            TreeNode * rootNode = myStack.top();
            while(rootNode->left){
                rootNode = rootNode->left;
                myStack.push(rootNode);
            }
            
            TreeNode * node = myStack.pop();
            res.push_back(node->val);
         
        }
        
        return res;
    }
};